refactor: inherit blob metadata for computed projections

python/python/lancedb/remote/table.py

@@ -67,7 +67,15 @@ from ..query import (
     LanceTakeQueryBuilder,
     LanceVectorQueryBuilder,
 )
-from ..table import AsyncTable, BlobMode, Branches, IndexStatistics, Query, Table, Tags
+from ..table import (
+    AsyncTable,
+    BlobMode,
+    Branches,
+    IndexStatistics,
+    Query,
+    Table,
+    Tags,
+)
 from ..types import BaseTokenizerType
 
 

python/python/lancedb/table.py

@@ -2165,9 +2165,11 @@ class Table(ABC):
             Function columns are supported only on LanceDB Cloud and
             Enterprise.
         computed: Dict[str, str], optional
-            A map of column name to a SQL expression defining the column. The
-            column's type and inputs are derived from the expression, so no
-            data type is supplied.
+            A mapping from output column names to SQL expressions derives each
+            output field from its expression. A direct projection of a Blob v2
+            field inherits Blob v2 semantics; other expressions derive their
+            ordinary Arrow type. Mapping order is declaration and dependency
+            order.
 
             Unlike ``transforms``, the expression is stored rather than
             evaluated now: the column is committed with no values, and rows get
@@ -6268,8 +6270,11 @@ class AsyncTable:
             Function columns are supported only on LanceDB Cloud and
             Enterprise.
         computed: Dict[str, str], optional
-            A map of column name to a SQL expression defining the column. The
-            column's type and inputs are derived from the expression.
+            A mapping from output column names to SQL expressions derives each
+            output field from its expression. A direct projection of a Blob v2
+            field inherits Blob v2 semantics; other expressions derive their
+            ordinary Arrow type. Mapping order is declaration and dependency
+            order.
 
             Unlike ``transforms``, the expression is stored rather than
             evaluated now: the column is committed with no values, and rows get

python/python/tests/test_table.py

@@ -4087,6 +4087,29 @@ def test_computed_column_rejects_transforms_and_computed_together(tmp_path):
         table.add_columns({"a": "x + 1"}, computed={"b": "x * 2"})
 
 
+def test_computed_column_blob_projection_inherits_semantics(tmp_path):
+    schema = pa.schema([pa.field("id", pa.int64()), lancedb.blob("image")])
+    db = lancedb.connect(tmp_path)
+    table = db.create_table("computed_column_blob", schema=schema)
+    table.add(
+        [
+            {"id": 1, "image": b"hello"},
+            {"id": 2, "image": b""},
+            {"id": 3, "image": None},
+        ]
+    )
+
+    table.add_columns(computed={"image_copy": "image", "second_copy": "image_copy"})
+    assert table.refresh_column("image_copy").rows_filled == 2
+    assert table.refresh_column("second_copy").rows_filled == 2
+    assert table.blob_columns() == ["image", "image_copy", "second_copy"]
+
+    hits = table.search().with_row_id(True).limit(10).to_arrow()
+    rows = sorted(zip(hits["id"].to_pylist(), hits["_rowid"].to_pylist()))
+    copied = table.fetch_blobs("second_copy", [row_id for _, row_id in rows])
+    assert copied.to_pylist() == [b"hello", b"", None]
+
+
 @pytest.mark.asyncio
 async def test_computed_column_async(tmp_path):
     db = await lancedb.connect_async(tmp_path)

rust/lancedb/src/remote/table.rs

@@ -3180,8 +3180,8 @@ impl<S: HttpSend> BaseTable for RemoteTable<S> {
             self.schema().await?.as_ref(),
             "schema evolution",
         )?;
-        // The server plans the declaration: expression validation, type
-        // inference and the persisted binding all happen there.
+        // The server plans the declaration against its table schema, including
+        // Blob v2 semantics inherited by a direct field projection.
         let entries = columns
             .iter()
             .map(
@@ -7388,8 +7388,8 @@ mod tests {
         assert_eq!(result.version, if old_server { 0 } else { 43 });
     }
 
-    /// A declaration is sent as `{name, computed}` entries for the server to
-    /// plan; the client never types the expression itself.
+    /// A declaration is sent as `{name, computed}` for the server to plan; the
+    /// client never types the expression itself.
     #[tokio::test]
     async fn test_add_computed_columns_sends_the_expression() {
         let table = Table::new_with_handler("my_table", |request| match request.url().path() {

rust/lancedb/src/table.rs

@@ -750,8 +750,8 @@ pub trait BaseTable: std::fmt::Display + std::fmt::Debug + Send + Sync {
     /// Declare computed columns, each defined by a SQL expression.
     ///
     /// Where the declaration is planned depends on the backend: a local table
-    /// validates and types the expression itself, a remote one sends the text
-    /// for the server to plan.
+    /// validates and types the expression itself, while a remote one sends the
+    /// expression for the server to plan.
     async fn add_computed_columns(
         &self,
         _columns: &[(String, String)],

rust/lancedb/src/table/computed_columns.rs

@@ -9,29 +9,35 @@
 //! refresh fills the rows.
 //!
 //! The rule is tagged by kind ([`ComputedColumnKind`]) because kinds differ in
-//! where the column's type and inputs come from. A SQL expression is
-//! self-describing -- both are derived from the expression, so a caller writes
-//! neither -- while a kind resolved through a registry cannot be typed without
-//! consulting it. Registered Functions use an exact remote version plus a
-//! schema-level Function binding; unknown newer kinds remain readable and fail
-//! closed before mutation.
+//! where the column's type and inputs come from. A SQL expression determines
+//! its inputs and physical result type. A direct projection of a Blob v2 field
+//! also inherits that field's semantic type while execution continues to use
+//! `LargeBinary`. A kind resolved through a registry cannot be typed without
+//! consulting it.
+//! Registered Functions use an exact remote version plus a schema-level
+//! Function binding; unknown newer kinds remain readable and fail closed
+//! before mutation.
 //!
 //! [`computed_columns`] and [`computed_column_from_field`] read declarations
 //! back off a schema.
 
-use std::collections::{BTreeSet, HashMap};
+use std::collections::{BTreeSet, HashMap, HashSet};
 use std::sync::Arc;
 
 use arrow_schema::{DataType, Field as ArrowField, Fields, Schema as ArrowSchema, SchemaRef};
-use datafusion_common::tree_node::TreeNode;
+use datafusion_common::{ScalarValue, tree_node::TreeNode};
+use datafusion_expr::Expr;
 use datafusion_physical_plan::PhysicalExpr;
 use lance::dataset::NewColumnTransform;
+use lance_arrow::FieldExt;
+use lance_core::datatypes::{BLOB_V2_DESC_FIELD, format_field_path_minimal, parse_field_path};
 use lance_datafusion::planner::Planner;
 use lance_namespace::models::{JsonArrowDataType, JsonArrowField, JsonArrowSchema};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
 use crate::function::{FunctionApplication, FunctionBinding};
+use crate::utils::resolve_arrow_field_path;
 use crate::{Error, Result};
 
 /// Field metadata key marking a column as computed. The value is `"true"`.
@@ -1106,15 +1112,20 @@ pub(crate) fn ensure_no_foreign_declarations<'a>(
     fields: impl IntoIterator<Item = &'a Arc<ArrowField>>,
 ) -> Result<()> {
     for field in fields {
-        if field.metadata().keys().any(|k| is_declaration_key(k)) {
-            return Err(Error::InvalidInput {
-                message: format!(
-                    "field '{}' carries computed-column metadata; declare computed columns \
-                     with add_columns().computed()",
-                    field.name()
-                ),
-            });
-        }
+        ensure_no_foreign_declaration(field)?;
+    }
+    Ok(())
+}
+
+fn ensure_no_foreign_declaration(field: &ArrowField) -> Result<()> {
+    if field.metadata().keys().any(|k| is_declaration_key(k)) {
+        return Err(Error::InvalidInput {
+            message: format!(
+                "field '{}' carries computed-column metadata; declare computed columns \
+                 with add_columns().computed()",
+                field.name()
+            ),
+        });
     }
     Ok(())
 }
@@ -1162,15 +1173,154 @@ pub(crate) struct BoundExpression {
     /// The columns the expression names, as written; nested inputs keep
     /// their dotted path.
     pub inputs: Vec<String>,
-    /// The top-level columns evaluation reads, in [`Self::read_schema`]
-    /// order. A nested input appears through its root.
+    /// The top-level columns evaluation reads, in physical-expression order.
+    /// A nested input appears through its root.
     pub roots: Vec<String>,
-    /// The projected schema evaluation runs against.
-    pub read_schema: SchemaRef,
     /// The compiled expression.
     pub physical: Arc<dyn PhysicalExpr>,
     /// The type the expression yields.
     pub data_type: DataType,
+    /// Blob v2 leaves the scan must materialize as `LargeBinary`.
+    pub blob_paths: Vec<String>,
+    /// A directly projected Blob v2 field whose semantics the output inherits.
+    projected_blob_field: Option<ArrowField>,
+}
+
+fn is_direct_field_projection(expr: &Expr) -> bool {
+    match expr {
+        Expr::Column(_) => true,
+        Expr::ScalarFunction(function)
+            if function.name() == "get_field" && function.args.len() == 2 =>
+        {
+            is_direct_field_projection(&function.args[0])
+                && matches!(
+                    &function.args[1],
+                    Expr::Literal(ScalarValue::Utf8(Some(_)), _)
+                )
+        }
+        _ => false,
+    }
+}
+
+fn projected_blob_field(schema: &ArrowSchema, expr: &Expr) -> Result<Option<ArrowField>> {
+    if !is_direct_field_projection(expr) {
+        return Ok(None);
+    }
+    let paths = Planner::column_names_in_expr(expr);
+    let [path] = paths.as_slice() else {
+        return Ok(None);
+    };
+    let (_, field) = resolve_arrow_field_path(schema, path)?;
+    Ok(field.is_blob_v2().then_some(field))
+}
+
+fn collect_blob_paths(field: &ArrowField, parent: &[String], paths: &mut Vec<Vec<String>>) {
+    let mut path = parent.to_vec();
+    path.push(field.name().clone());
+    if field.is_blob_v2() {
+        paths.push(path);
+        return;
+    }
+    match field.data_type() {
+        DataType::Struct(children) => {
+            for child in children {
+                collect_blob_paths(child, &path, paths);
+            }
+        }
+        DataType::List(child)
+        | DataType::LargeList(child)
+        | DataType::FixedSizeList(child, _)
+        | DataType::Map(child, _) => collect_blob_paths(child, &path, paths),
+        _ => {}
+    }
+}
+
+fn schema_blob_paths(schema: &ArrowSchema) -> Vec<Vec<String>> {
+    let mut paths = Vec::new();
+    for field in schema.fields() {
+        collect_blob_paths(field, &[], &mut paths);
+    }
+    paths
+}
+
+fn transform_blob_field(
+    field: &ArrowField,
+    parent: &[String],
+    materialized: &HashSet<Vec<String>>,
+) -> ArrowField {
+    let mut path = parent.to_vec();
+    path.push(field.name().clone());
+    if field.is_blob_v2() {
+        if materialized.contains(&path) {
+            return ArrowField::new(field.name(), DataType::LargeBinary, field.is_nullable());
+        }
+        return ArrowField::new(
+            field.name(),
+            BLOB_V2_DESC_FIELD.data_type().clone(),
+            field.is_nullable(),
+        )
+        .with_metadata(BLOB_V2_DESC_FIELD.metadata().clone());
+    }
+
+    let data_type = match field.data_type() {
+        DataType::Struct(children) => DataType::Struct(
+            children
+                .iter()
+                .map(|child| Arc::new(transform_blob_field(child, &path, materialized)))
+                .collect(),
+        ),
+        DataType::List(child) => {
+            DataType::List(Arc::new(transform_blob_field(child, &path, materialized)))
+        }
+        DataType::LargeList(child) => {
+            DataType::LargeList(Arc::new(transform_blob_field(child, &path, materialized)))
+        }
+        DataType::FixedSizeList(child, size) => DataType::FixedSizeList(
+            Arc::new(transform_blob_field(child, &path, materialized)),
+            *size,
+        ),
+        DataType::Map(child, sorted) => DataType::Map(
+            Arc::new(transform_blob_field(child, &path, materialized)),
+            *sorted,
+        ),
+        _ => return field.clone(),
+    };
+    ArrowField::new(field.name(), data_type, field.is_nullable())
+        .with_metadata(field.metadata().clone())
+}
+
+fn blob_runtime_schema(schema: &ArrowSchema, materialized: &HashSet<Vec<String>>) -> SchemaRef {
+    Arc::new(ArrowSchema::new_with_metadata(
+        schema
+            .fields()
+            .iter()
+            .map(|field| Arc::new(transform_blob_field(field, &[], materialized)))
+            .collect::<Fields>(),
+        schema.metadata().clone(),
+    ))
+}
+
+fn referenced_blob_paths(schema: &ArrowSchema, inputs: &[String]) -> Result<Vec<Vec<String>>> {
+    let input_paths = inputs
+        .iter()
+        .map(|input| {
+            parse_field_path(input).map_err(|error| Error::InvalidInput {
+                message: format!("invalid computed-column input path '{input}': {error}"),
+            })
+        })
+        .collect::<Result<Vec<_>>>()?;
+    Ok(schema_blob_paths(schema)
+        .into_iter()
+        .filter(|blob_path| {
+            input_paths.iter().any(|input_path| {
+                input_path.len() <= blob_path.len()
+                    && input_path
+                        .iter()
+                        .zip(blob_path)
+                        .all(|(input, blob)| input == blob)
+            })
+        })
+        .collect())
 }
 
 /// Parse, resolve and compile `expression` against `schema`.
@@ -1185,10 +1335,18 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
         message,
     };
 
-    let planner = Planner::new(schema.clone());
+    // Blob v2 is a semantic type whose runtime expression ABI is
+    // `LargeBinary`. Parse against that ABI first so a direct Blob reference
+    // is not mistaken for its storage descriptor struct.
+    let all_blob_paths = schema_blob_paths(schema.as_ref())
+        .into_iter()
+        .collect::<HashSet<_>>();
+    let parsing_schema = blob_runtime_schema(schema.as_ref(), &all_blob_paths);
+    let planner = Planner::new(parsing_schema);
     let parsed = planner
         .parse_expr(expression)
         .map_err(|e| invalid(e.to_string()))?;
+    let projected_blob_field = projected_blob_field(schema.as_ref(), &parsed)?;
 
     // A declaration is evaluated more than once -- staging and writing are
     // separate passes, and a refresh years later replays the same text -- so
@@ -1218,13 +1376,19 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
     inputs.sort();
     inputs.dedup();
 
+    let blob_paths = referenced_blob_paths(schema.as_ref(), &inputs)?;
+    let runtime_schema = blob_runtime_schema(
+        schema.as_ref(),
+        &blob_paths.iter().cloned().collect::<HashSet<_>>(),
+    );
+
     // A nested input is recorded by its path but read through its root
     // column; Schema::index_of resolves top-level names only. Resolved here
     // rather than left to the planner so an unknown column names itself in
     // the error instead of surfacing as a plan failure.
     let mut indices = Vec::with_capacity(inputs.len());
     for input in &inputs {
-        let index = schema
+        let index = runtime_schema
             .index_of(root(input))
             .map_err(|_| invalid(format!("unknown column '{input}'")))?;
         if !indices.contains(&index) {
@@ -1237,7 +1401,7 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
     // compiles the expression has to be built on the projected schema
     // evaluation will actually read.
     let read_schema = Arc::new(
-        schema
+        runtime_schema
             .project(&indices)
             .map_err(|e| invalid(e.to_string()))?,
     );
@@ -1247,7 +1411,8 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
         .map(|field| field.name().clone())
         .collect();
 
-    let optimized = planner
+    let runtime_planner = Planner::new(runtime_schema);
+    let optimized = runtime_planner
         .optimize_expr(parsed)
         .map_err(|e| invalid(e.to_string()))?;
     let physical = Planner::new(read_schema.clone())
@@ -1260,9 +1425,16 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
     Ok(BoundExpression {
         inputs,
         roots,
-        read_schema,
         physical,
         data_type,
+        blob_paths: blob_paths
+            .iter()
+            .map(|path| {
+                let segments = path.iter().map(String::as_str).collect::<Vec<_>>();
+                format_field_path_minimal(&segments)
+            })
+            .collect(),
+        projected_blob_field,
     })
 }
 
@@ -1278,7 +1450,7 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
 /// batch may declare `a` and then `b = a + 1` in one commit. Refresh order
 /// then matters, and refresh enforces it: `b` is refused while `a` still has
 /// unfilled rows.
-pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Vec<ArrowField>> {
+fn plan_declarations(schema: SchemaRef, columns: &[(String, String)]) -> Result<Vec<ArrowField>> {
     if columns.is_empty() {
         return Err(Error::InvalidInput {
             message: "at least one computed column is required".into(),
@@ -1290,15 +1462,28 @@ pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Ve
 
     for (name, expression) in columns {
         if schema.field_with_name(name).is_ok() {
-            return Err(Error::ColumnAlreadyExists { name: name.clone() });
+            return Err(Error::ColumnAlreadyExists {
+                name: name.to_string(),
+            });
         }
 
         let bound = bind(schema.clone(), name, expression)?;
 
         // Declared columns start entirely null, so nullability is a property
         // of the declaration rather than of what the expression yields.
-        let field = ArrowField::new(name, bound.data_type, true)
-            .with_metadata(computed_column_metadata(expression, &bound.inputs));
+        let computed_metadata = computed_column_metadata(expression, &bound.inputs);
+        let field = match bound.projected_blob_field {
+            Some(source) => {
+                let mut metadata = source.metadata().clone();
+                metadata.retain(|key, _| !is_declaration_key(key));
+                metadata.extend(computed_metadata);
+                source
+                    .with_name(name)
+                    .with_nullable(true)
+                    .with_metadata(metadata)
+            }
+            None => ArrowField::new(name, bound.data_type, true).with_metadata(computed_metadata),
+        };
         schema = Arc::new(ArrowSchema::new_with_metadata(
             schema
                 .fields()
@@ -1314,6 +1499,10 @@ pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Ve
     Ok(fields)
 }
 
+pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Vec<ArrowField>> {
+    plan_declarations(schema, columns)
+}
+
 /// Run the schema-level checks of
 /// [`AddColumnsBuilder::computed`](super::AddColumnsBuilder::computed) against
 /// `schema` without committing: the Function-binding guard and the planning of
@@ -1352,7 +1541,7 @@ pub(crate) fn declare(
     schema: SchemaRef,
     columns: &[(String, String)],
 ) -> Result<NewColumnTransform> {
-    let fields = plan(schema, columns)?;
+    let fields = plan_declarations(schema, columns)?;
     Ok(NewColumnTransform::AllNulls(Arc::new(ArrowSchema::new(
         fields,
     ))))
@@ -1478,6 +1667,44 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_direct_blob_projection_inherits_semantics() {
+        let schema = Arc::new(ArrowSchema::new(vec![crate::blob("image", false)]));
+        let fields = plan(
+            schema,
+            &[
+                ("first".to_string(), "image".to_string()),
+                ("second".to_string(), "first".to_string()),
+            ],
+        )
+        .unwrap();
+
+        for field in &fields {
+            assert!(field.is_blob_v2());
+            assert!(field.is_nullable());
+        }
+        assert_eq!(
+            fields[1]
+                .metadata()
+                .get(EXPRESSION_META_KEY)
+                .map(String::as_str),
+            Some("first")
+        );
+    }
+
+    #[test]
+    fn test_blob_expression_transformation_does_not_inherit_semantics() {
+        let schema = Arc::new(ArrowSchema::new(vec![crate::blob("image", true)]));
+        let fields = plan(
+            schema,
+            &[("payload".to_string(), "coalesce(image, image)".to_string())],
+        )
+        .unwrap();
+
+        assert!(!fields[0].is_blob_v2());
+        assert_eq!(fields[0].data_type(), &DataType::LargeBinary);
+    }
+
     /// The binding reaches the schema only if `AllNulls` carries per-field
     /// metadata through the commit. The whole representation rests on it.
     #[tokio::test]

rust/lancedb/src/table/refresh.rs

@@ -29,10 +29,14 @@
 //! inputs masked to null first, so a poison value in a row nobody is filling
 //! cannot fail the refresh.
 
+use std::collections::HashSet;
 use std::sync::Arc;
 
-use arrow_array::{ArrayRef, BooleanArray, RecordBatch, RecordBatchOptions};
-use arrow_schema::Schema as ArrowSchema;
+use arrow_array::{
+    Array, ArrayRef, BooleanArray, LargeBinaryArray, RecordBatch, RecordBatchOptions, StructArray,
+    new_null_array,
+};
+use arrow_schema::{DataType, Field as ArrowField, Schema as ArrowSchema};
 use datafusion_expr::ColumnarValue;
 use futures::{Stream, StreamExt, TryStreamExt};
 use lance::Dataset;
@@ -40,7 +44,7 @@ use lance::dataset::WriteDestination;
 use lance::dataset::fragment::FileFragment;
 use lance::dataset::transaction::Operation;
 use lance_core::ROW_ID;
-use lance_core::datatypes::Schema as LanceSchema;
+use lance_core::datatypes::{BlobHandling, Schema as LanceSchema};
 use serde::{Deserialize, Serialize};
 
 use super::computed_columns::{BoundExpression, ComputedColumnKind, computed_column_from_field};
@@ -104,6 +108,7 @@ async fn execute_refresh_column_with_source(
         fields: vec![field.clone()],
         metadata: Default::default(),
     };
+    let output_is_blob = field.is_blob_v2();
 
     let mut rows_filled = 0u64;
     let mut replacements = Vec::new();
@@ -113,7 +118,8 @@ async fn execute_refresh_column_with_source(
             continue;
         }
         rows_filled += gained;
-        let values = fill_stream(&dataset, &fragment, bound.clone(), column).await?;
+        let values =
+            fill_stream(&dataset, &fragment, bound.clone(), column, output_is_blob).await?;
         replacements.push(fragment.write_columns(values, &column_schema).await?);
     }
 
@@ -294,12 +300,15 @@ fn evaluation_batch(
     mask_out: Option<&BooleanArray>,
 ) -> lance_core::Result<RecordBatch> {
     let mut columns = Vec::with_capacity(bound.roots.len());
+    let mut fields = Vec::with_capacity(bound.roots.len());
     for name in &bound.roots {
-        let column = batch.column_by_name(name).ok_or_else(|| {
+        let index = batch.schema_ref().index_of(name).map_err(|_| {
             lance_core::Error::invalid_input(format!(
                 "refreshing a computed column read no {name} column"
             ))
         })?;
+        let column = batch.column(index);
+        fields.push(batch.schema_ref().field(index).clone());
         // Rows outside the mask must not reach the expression: a value in a
         // deleted or already-filled row can be one it would choke on.
         columns.push(match mask_out {
@@ -308,7 +317,7 @@ fn evaluation_batch(
         });
     }
     Ok(RecordBatch::try_new_with_options(
-        bound.read_schema.clone(),
+        Arc::new(ArrowSchema::new(fields)),
         columns,
         &RecordBatchOptions::new().with_row_count(Some(batch.num_rows())),
     )?)
@@ -329,6 +338,99 @@ fn evaluate(bound: &BoundExpression, batch: &RecordBatch) -> lance_core::Result<
     }
 }
 
+fn materialized_blob_ids(schema: &LanceSchema, paths: &[String]) -> Result<HashSet<u32>> {
+    paths
+        .iter()
+        .map(|path| {
+            let field = schema
+                .resolve(path)
+                .and_then(|fields| fields.last().copied())
+                .ok_or_else(|| Error::InvalidInput {
+                    message: format!("computed Blob input '{path}' no longer exists"),
+                })?;
+            if !field.is_blob_v2() {
+                return Err(Error::InvalidInput {
+                    message: format!("computed Blob input '{path}' is no longer Blob v2"),
+                });
+            }
+            u32::try_from(field.id).map_err(|_| Error::InvalidInput {
+                message: format!(
+                    "computed Blob input '{path}' has invalid field id {}",
+                    field.id
+                ),
+            })
+        })
+        .collect()
+}
+
+fn configure_blob_inputs(
+    scanner: &mut lance::dataset::scanner::Scanner,
+    schema: &LanceSchema,
+    bound: &BoundExpression,
+    extra_blob_id: Option<u32>,
+) -> Result<()> {
+    let mut ids = materialized_blob_ids(schema, &bound.blob_paths)?;
+    ids.extend(extra_blob_id);
+    scanner.blob_handling(BlobHandling::SomeBlobsBinary(ids));
+    Ok(())
+}
+
+fn blob_array_from_binary(
+    array: &ArrayRef,
+    target_field: &ArrowField,
+) -> lance_core::Result<ArrayRef> {
+    let values = array
+        .as_any()
+        .downcast_ref::<LargeBinaryArray>()
+        .ok_or_else(|| {
+            lance_core::Error::invalid_input(format!(
+                "a Blob v2 computed output produced {}, expected LargeBinary",
+                array.data_type()
+            ))
+        })?;
+    let mut builder = lance::blob::BlobArrayBuilder::new(values.len());
+    for index in 0..values.len() {
+        if values.is_null(index) {
+            builder.push_null()?;
+        } else {
+            builder.push_bytes(values.value(index))?;
+        }
+    }
+    let minimal = builder.finish()?;
+    let minimal = minimal
+        .as_any()
+        .downcast_ref::<StructArray>()
+        .ok_or_else(|| lance_core::Error::internal("Blob builder returned a non-struct array"))?;
+    let DataType::Struct(target_fields) = target_field.data_type() else {
+        return Err(lance_core::Error::invalid_input(format!(
+            "Blob v2 output field '{}' has non-struct type {}",
+            target_field.name(),
+            target_field.data_type()
+        )));
+    };
+    let columns = target_fields
+        .iter()
+        .map(|field| match field.name().as_str() {
+            "data" | "uri" => minimal
+                .column_by_name(field.name())
+                .cloned()
+                .ok_or_else(|| {
+                    lance_core::Error::internal(format!("Blob builder omitted '{}'", field.name()))
+                }),
+            "position" | "size" => Ok(new_null_array(field.data_type(), minimal.len())),
+            name => Err(lance_core::Error::invalid_input(format!(
+                "Blob v2 output field '{}' has unsupported logical child '{name}'",
+                target_field.name()
+            ))),
+        })
+        .collect::<lance_core::Result<Vec<_>>>()?;
+    Ok(Arc::new(StructArray::try_new(
+        target_fields.clone(),
+        columns,
+        minimal.nulls().cloned(),
+    )?))
+}
+
 /// How many rows of one fragment would gain a value.
 ///
 /// Scans only the unfilled live rows -- deleted rows never reach the
@@ -347,6 +449,7 @@ async fn count_fragment_gains(
         .with_row_id()
         .filter(&format!("{} IS NULL", quote_identifier(column)))?
         .project(&bound.roots)?;
+    configure_blob_inputs(&mut scanner, dataset.schema(), bound, None)?;
 
     let mut gained = 0u64;
     let mut batches = scanner.try_into_stream().await?;
@@ -368,6 +471,7 @@ async fn fill_stream(
     fragment: &FileFragment,
     bound: Arc<BoundExpression>,
     column: &str,
+    output_is_blob: bool,
 ) -> Result<impl Stream<Item = lance_core::Result<RecordBatch>> + Send + use<>> {
     let mut projection: Vec<String> = bound.roots.clone();
     projection.push(column.to_string());
@@ -377,6 +481,20 @@ async fn fill_stream(
         .with_row_id()
         .include_deleted_rows()
         .project(&projection)?;
+    let output_blob_id = output_is_blob
+        .then(|| {
+            dataset
+                .schema()
+                .field(column)
+                .and_then(|field| u32::try_from(field.id).ok())
+        })
+        .flatten();
+    configure_blob_inputs(
+        &mut scanner,
+        dataset.schema(),
+        bound.as_ref(),
+        output_blob_id,
+    )?;
 
     let projected = Arc::new(ArrowSchema::new(vec![
         ArrowSchema::from(dataset.schema())
@@ -412,6 +530,11 @@ async fn fill_stream(
 
         let computed = evaluate(&bound, &evaluation_batch(&batch, &bound, Some(&keep))?)?;
         let merged = arrow_select::zip::zip(&fill, &computed, existing)?;
+        let merged = if output_is_blob {
+            blob_array_from_binary(&merged, projected.field(0))?
+        } else {
+            merged
+        };
         Ok(RecordBatch::try_new(projected.clone(), vec![merged])?)
     }))
 }
@@ -420,8 +543,12 @@ async fn fill_stream(
 mod tests {
     use std::sync::Arc;
 
-    use arrow_array::{Int32Array, record_batch};
+    use arrow_array::{
+        Array, ArrayRef, Int32Array, LargeBinaryArray, RecordBatch, StructArray, record_batch,
+    };
+    use arrow_schema::Field as ArrowField;
     use futures::TryStreamExt;
+    use lance_core::ROW_ID;
 
     use crate::connect;
     use crate::query::{ExecutableQuery, QueryBase, Select};
@@ -477,6 +604,25 @@ mod tests {
         table.add(batch).execute().await.unwrap();
     }
 
+    #[test]
+    fn test_blob_output_matches_complete_logical_field() {
+        let values: ArrayRef = Arc::new(LargeBinaryArray::from(vec![
+            Some(b"hello".as_slice()),
+            None,
+        ]));
+        let field = ArrowField::new(
+            "image",
+            lance_core::datatypes::BLOB_V2_LOGICAL_TYPE.clone(),
+            true,
+        );
+
+        let output = super::blob_array_from_binary(&values, &field).unwrap();
+        assert_eq!(output.data_type(), field.data_type());
+        let output = output.as_any().downcast_ref::<StructArray>().unwrap();
+        assert_eq!(output.column_by_name("position").unwrap().null_count(), 2);
+        assert_eq!(output.column_by_name("size").unwrap().null_count(), 2);
+    }
+
     /// The gate's reproducer: `b = coalesce(a, 0)` refreshed before `a`
     /// must not bake zeros from `a`'s placeholder null. It is refused, and
     /// names the input, until `a` is filled -- after every append too.
@@ -1164,4 +1310,366 @@ mod tests {
         let err = table.refresh_column("embedding").await.unwrap_err();
         assert!(matches!(err, Error::NotSupported { message } if message.contains("udf")));
     }
+
+    fn blob_batch(ids: Vec<i32>, payloads: Vec<Option<&[u8]>>) -> RecordBatch {
+        use arrow_array::Int32Array;
+        use arrow_schema::{Field, Schema};
+
+        let mut builder = lance::blob::BlobArrayBuilder::new(payloads.len());
+        for payload in payloads {
+            match payload {
+                Some(payload) => builder.push_bytes(payload).unwrap(),
+                None => builder.push_null().unwrap(),
+            }
+        }
+        RecordBatch::try_new(
+            Arc::new(Schema::new(vec![
+                Field::new("id", arrow_schema::DataType::Int32, false),
+                crate::blob("image", true),
+            ])),
+            vec![Arc::new(Int32Array::from(ids)), builder.finish().unwrap()],
+        )
+        .unwrap()
+    }
+
+    async fn create_blob_table(path: &std::path::Path, batch: RecordBatch) -> Table {
+        let conn = connect(path.to_str().unwrap()).execute().await.unwrap();
+        conn.create_table("blobs", batch).execute().await.unwrap()
+    }
+
+    #[tokio::test]
+    async fn test_refresh_inherits_and_publishes_blob_output() {
+        use arrow_array::UInt64Array;
+        use lance_arrow::{
+            BLOB_DEDICATED_SIZE_THRESHOLD_META_KEY, BLOB_INLINE_SIZE_THRESHOLD_META_KEY,
+        };
+        use lance_core::datatypes::BlobKind;
+
+        use crate::table::schema_evolution::FieldMetadataUpdate;
+
+        let tmp = tempfile::tempdir().unwrap();
+        let table = create_blob_table(
+            tmp.path(),
+            blob_batch(
+                vec![1, 2, 3, 4],
+                vec![Some(b"hello"), Some(b"ab"), Some(b""), None],
+            ),
+        )
+        .await;
+        table
+            .add_columns()
+            .computed("image_copy", "image")
+            .execute()
+            .await
+            .unwrap();
+        table
+            .update_field_metadata(&[FieldMetadataUpdate::new("image_copy")
+                .set(BLOB_INLINE_SIZE_THRESHOLD_META_KEY, "1")
+                .set(BLOB_DEDICATED_SIZE_THRESHOLD_META_KEY, "4")])
+            .await
+            .unwrap();
+
+        let first_refresh = table.refresh_column("image_copy").await.unwrap();
+        assert_eq!(first_refresh.rows_filled, 3);
+        assert_eq!(
+            table.blob_columns().await.unwrap(),
+            vec!["image".to_string(), "image_copy".to_string()]
+        );
+
+        let batches = table
+            .query()
+            .with_row_id()
+            .execute()
+            .await
+            .unwrap()
+            .try_collect::<Vec<_>>()
+            .await
+            .unwrap();
+        let batch = arrow_select::concat::concat_batches(&batches[0].schema(), &batches).unwrap();
+        assert!(
+            batch
+                .column_by_name("image_copy")
+                .unwrap()
+                .as_any()
+                .is::<arrow_array::StructArray>()
+        );
+        let row_ids = batch
+            .column_by_name(ROW_ID)
+            .unwrap()
+            .as_any()
+            .downcast_ref::<UInt64Array>()
+            .unwrap()
+            .values()
+            .to_vec();
+        let original = table.fetch_blobs("image", &row_ids).await.unwrap();
+        let copied = table.fetch_blobs("image_copy", &row_ids).await.unwrap();
+        assert_eq!(original, copied);
+        let ids = batch
+            .column_by_name("id")
+            .unwrap()
+            .as_any()
+            .downcast_ref::<Int32Array>()
+            .unwrap();
+        let files = table
+            .fetch_blob_files("image_copy", &row_ids)
+            .await
+            .unwrap();
+        let mut layouts = ids
+            .values()
+            .iter()
+            .copied()
+            .zip(files)
+            .map(|(id, file)| (id, file.and_then(|file| file.kind())))
+            .collect::<Vec<_>>();
+        layouts.sort_by_key(|(id, _)| *id);
+        assert_eq!(
+            layouts,
+            vec![
+                (1, Some(BlobKind::Dedicated)),
+                (2, Some(BlobKind::Packed)),
+                (3, Some(BlobKind::Inline)),
+                (4, None),
+            ]
+        );
+
+        table
+            .add(blob_batch(vec![5], vec![Some(b"appended")]))
+            .execute()
+            .await
+            .unwrap();
+        table
+            .optimize(crate::table::OptimizeAction::Compact {
+                options: crate::table::CompactionOptions::default(),
+                remap_options: None,
+            })
+            .await
+            .unwrap();
+        assert_eq!(
+            table
+                .refresh_column("image_copy")
+                .await
+                .unwrap()
+                .rows_filled,
+            1
+        );
+        assert_eq!(
+            table
+                .refresh_column("image_copy")
+                .await
+                .unwrap()
+                .rows_filled,
+            0
+        );
+
+        table.checkout(first_refresh.version).await.unwrap();
+        assert_eq!(table.count_rows(None).await.unwrap(), 4);
+        assert_eq!(
+            table.blob_columns().await.unwrap(),
+            vec!["image".to_string(), "image_copy".to_string()]
+        );
+        table.checkout_latest().await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn test_refresh_inherits_nested_struct_blob_input() {
+        use arrow_array::{Int32Array, StructArray, UInt64Array};
+        use arrow_schema::{DataType, Field, Fields, Schema};
+
+        let tmp = tempfile::tempdir().unwrap();
+        let mut blob_builder = lance::blob::BlobArrayBuilder::new(2);
+        blob_builder.push_bytes(b"nested").unwrap();
+        blob_builder.push_null().unwrap();
+        let blob_field = crate::blob("image", true);
+        let metadata_fields = Fields::from(vec![blob_field.clone()]);
+        let metadata = StructArray::new(
+            metadata_fields.clone(),
+            vec![blob_builder.finish().unwrap()],
+            None,
+        );
+        let batch = RecordBatch::try_new(
+            Arc::new(Schema::new(vec![
+                Field::new("id", DataType::Int32, false),
+                Field::new("metadata", DataType::Struct(metadata_fields), true),
+            ])),
+            vec![Arc::new(Int32Array::from(vec![1, 2])), Arc::new(metadata)],
+        )
+        .unwrap();
+        let table = create_blob_table(tmp.path(), batch).await;
+        table
+            .add_columns()
+            .computed("payload_copy", "metadata.image")
+            .execute()
+            .await
+            .unwrap();
+
+        assert_eq!(
+            table
+                .refresh_column("payload_copy")
+                .await
+                .unwrap()
+                .rows_filled,
+            1
+        );
+        assert_eq!(
+            table.blob_columns().await.unwrap(),
+            vec!["metadata.image".to_string(), "payload_copy".to_string()]
+        );
+        let batches = table
+            .query()
+            .with_row_id()
+            .execute()
+            .await
+            .unwrap()
+            .try_collect::<Vec<_>>()
+            .await
+            .unwrap();
+        let row_ids = batches[0]
+            .column_by_name(ROW_ID)
+            .unwrap()
+            .as_any()
+            .downcast_ref::<UInt64Array>()
+            .unwrap()
+            .values();
+        let payloads = table.fetch_blobs("payload_copy", row_ids).await.unwrap();
+        assert_eq!(payloads.value(0), b"nested");
+        assert!(payloads.is_null(1));
+    }
+
+    #[tokio::test]
+    async fn test_refresh_preserves_list_shape_when_materializing_blob_input() {
+        use arrow_array::{Int32Array, ListArray};
+        use arrow_buffer::{OffsetBuffer, ScalarBuffer};
+        use arrow_schema::{DataType, Field, Schema};
+
+        let tmp = tempfile::tempdir().unwrap();
+        let mut blob_builder = lance::blob::BlobArrayBuilder::new(3);
+        blob_builder.push_bytes(b"a").unwrap();
+        blob_builder.push_bytes(b"bb").unwrap();
+        blob_builder.push_null().unwrap();
+        let item = Arc::new(crate::blob("item", true));
+        let images = ListArray::new(
+            item.clone(),
+            OffsetBuffer::new(ScalarBuffer::from(vec![0, 2, 3])),
+            blob_builder.finish().unwrap(),
+            None,
+        );
+        let batch = RecordBatch::try_new(
+            Arc::new(Schema::new(vec![
+                Field::new("id", DataType::Int32, false),
+                Field::new("images", DataType::List(item), true),
+            ])),
+            vec![Arc::new(Int32Array::from(vec![1, 2])), Arc::new(images)],
+        )
+        .unwrap();
+        let table = create_blob_table(tmp.path(), batch).await;
+        table
+            .add_columns()
+            .computed("image_payloads", "images")
+            .execute()
+            .await
+            .unwrap();
+
+        assert_eq!(
+            table
+                .refresh_column("image_payloads")
+                .await
+                .unwrap()
+                .rows_filled,
+            2
+        );
+        let batches = table
+            .query()
+            .select(Select::columns(&["image_payloads"]))
+            .execute()
+            .await
+            .unwrap()
+            .try_collect::<Vec<_>>()
+            .await
+            .unwrap();
+        let output = batches[0]
+            .column_by_name("image_payloads")
+            .unwrap()
+            .as_any()
+            .downcast_ref::<ListArray>()
+            .unwrap();
+        assert_eq!(output.value_offsets(), &[0, 2, 3]);
+        assert!(output.values().as_any().is::<LargeBinaryArray>());
+    }
+
+    #[tokio::test]
+    async fn test_refresh_inherits_external_blob_input() {
+        use arrow_array::{Int32Array, StringArray, UInt64Array};
+        use arrow_schema::{DataType, Field, Schema};
+
+        let tmp = tempfile::tempdir().unwrap();
+        let payload = b"external-payload";
+        let path = tmp.path().join("payload.bin");
+        std::fs::write(&path, payload).unwrap();
+        let uri = url::Url::from_file_path(path).unwrap().to_string();
+        let conn = connect(tmp.path().join("db").to_str().unwrap())
+            .execute()
+            .await
+            .unwrap();
+        let table = conn
+            .create_empty_table(
+                "external",
+                Arc::new(Schema::new(vec![
+                    Field::new("id", DataType::Int32, false),
+                    crate::blob("image", true),
+                ])),
+            )
+            .execute()
+            .await
+            .unwrap();
+        let batch = RecordBatch::try_new(
+            Arc::new(Schema::new(vec![
+                Field::new("id", DataType::Int32, false),
+                Field::new("image", DataType::Utf8, true),
+            ])),
+            vec![
+                Arc::new(Int32Array::from(vec![1])),
+                Arc::new(StringArray::from(vec![Some(uri)])),
+            ],
+        )
+        .unwrap();
+        table
+            .add(batch)
+            .allow_external_blob_outside_bases(true)
+            .execute()
+            .await
+            .unwrap();
+        table
+            .add_columns()
+            .computed("payload_copy", "image")
+            .execute()
+            .await
+            .unwrap();
+
+        assert_eq!(
+            table
+                .refresh_column("payload_copy")
+                .await
+                .unwrap()
+                .rows_filled,
+            1
+        );
+        let batches = table
+            .query()
+            .with_row_id()
+            .execute()
+            .await
+            .unwrap()
+            .try_collect::<Vec<_>>()
+            .await
+            .unwrap();
+        let row_ids = batches[0]
+            .column_by_name(ROW_ID)
+            .unwrap()
+            .as_any()
+            .downcast_ref::<UInt64Array>()
+            .unwrap()
+            .values();
+        let payloads = table.fetch_blobs("payload_copy", row_ids).await.unwrap();
+        assert_eq!(payloads.value(0), payload);
+    }
 }