feat(rust): add datafusion catalog_provider through namespace

Cargo.toml

@@ -13,6 +13,7 @@ members = [
     "rust/lance-linalg",
     "rust/lance-namespace",
     "rust/lance-namespace-impls",
+    "rust/lance-namespace-datafusion",
     "rust/lance-table",
     "rust/lance-test-macros",
     "rust/lance-testing",

rust/lance-namespace-datafusion/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name = "lance-namespace-datafusion"
+description = "Lance namespace integration with Apache DataFusion catalogs and schemas"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+license.workspace = true
+repository.workspace = true
+keywords.workspace = true
+categories.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+async-trait.workspace = true
+dashmap = "6"
+datafusion.workspace = true
+lance.workspace = true
+lance-namespace.workspace = true
+tokio.workspace = true
+
+[dev-dependencies]
+arrow.workspace = true
+arrow-array.workspace = true
+arrow-schema.workspace = true
+datafusion-sql.workspace = true
+lance-namespace-impls.workspace = true
+tempfile.workspace = true
+
+[lints]
+workspace = true

rust/lance-namespace-datafusion/README.md

@@ -0,0 +1,46 @@
+# Lance Namespace-DataFusion Integration
+
+This crate provides a bridge between Lance Namespaces and Apache DataFusion, allowing Lance tables to be queried as if they were native DataFusion catalogs, schemas, and tables.
+
+It exposes a `SessionBuilder` that constructs a DataFusion `SessionContext` with `CatalogProvider` and `SchemaProvider` implementations backed by a `lance_namespace::LanceNamespace` instance.
+
+## Features
+
+- **Dynamic Catalogs**: Maps top-level Lance namespaces to DataFusion catalogs.
+- **Dynamic Schemas**: Maps child namespaces to DataFusion schemas.
+- **Lazy Table Loading**: Tables are loaded on-demand from the namespace when queried.
+- **Read-Only**: This integration focuses solely on providing read access (SQL `SELECT`) to Lance datasets. DML operations are not included.
+
+## Usage
+
+First, build a `LanceNamespace` (e.g., from a directory), then use the `SessionBuilder` to create a `SessionContext`.
+
+```rust,ignore
+use std::sync::Arc;
+use datafusion::prelude::SessionContext;
+use lance_namespace_datafusion::SessionBuilder;
+use lance_namespace::LanceNamespace;
+use lance_namespace_impls::DirectoryNamespaceBuilder;
+
+async fn run_query() {
+    // 1. Create a Lance Namespace
+    let temp_dir = tempfile::tempdir().unwrap();
+    let ns: Arc<dyn LanceNamespace> = Arc::new(
+        DirectoryNamespaceBuilder::new(temp_dir.path().to_string_lossy().to_string())
+            .build()
+            .await
+            .unwrap(),
+    );
+
+    // 2. Build a DataFusion SessionContext
+    let ctx = SessionBuilder::new()
+        .with_root(ns.into())
+        .build()
+        .await
+        .unwrap();
+
+    // 3. Run a SQL query
+    let df = ctx.sql("SELECT * FROM my_catalog.my_schema.my_table").await.unwrap();
+    df.show().await.unwrap();
+}
+```

rust/lance-namespace-datafusion/src/catalog.rs

@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The Lance Authors
+
+//! DataFusion catalog providers backed by Lance namespaces.
+
+use std::any::Any;
+use std::collections::HashSet;
+use std::sync::Arc;
+
+use dashmap::DashMap;
+use datafusion::catalog::{CatalogProvider, CatalogProviderList, SchemaProvider};
+use datafusion::error::Result;
+
+use crate::namespace_level::NamespaceLevel;
+use crate::schema::LanceSchemaProvider;
+#[allow(unused_imports)]
+use crate::SessionBuilder;
+
+/// A dynamic [`CatalogProviderList`] that maps Lance namespaces to catalogs.
+///
+/// The underlying namespace must be a four-level namespace. It is explicitly configured
+/// via [`SessionBuilder::with_root`], and each child namespace under this root is
+/// automatically registered as a [`LanceCatalogProvider`].
+#[derive(Debug, Clone)]
+pub struct LanceCatalogProviderList {
+    /// Root Lance namespace used to resolve catalogs / schemas / tables.
+    #[allow(dead_code)]
+    ns_level: NamespaceLevel,
+    /// Catalogs that have been loaded from the root namespace.
+    ///
+    /// Note: The values in this map may become stale over time, as there is currently
+    /// no mechanism to automatically refresh or invalidate cached catalog providers.
+    catalogs: DashMap<String, Arc<dyn CatalogProvider>>,
+}
+
+impl LanceCatalogProviderList {
+    pub async fn try_new(namespace: NamespaceLevel) -> Result<Self> {
+        let catalogs = DashMap::new();
+        for child_namespace in namespace.children().await? {
+            let catalog_name = child_namespace.name().to_string();
+            let catalog_provider = Arc::new(LanceCatalogProvider::try_new(child_namespace).await?);
+            catalogs.insert(catalog_name, catalog_provider as Arc<dyn CatalogProvider>);
+        }
+
+        Ok(Self {
+            ns_level: namespace,
+            catalogs,
+        })
+    }
+}
+
+impl CatalogProviderList for LanceCatalogProviderList {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    /// Adds a new catalog to this catalog list.
+    /// If a catalog of the same name existed before, it is replaced in the list and returned.
+    fn register_catalog(
+        &self,
+        name: String,
+        catalog: Arc<dyn CatalogProvider>,
+    ) -> Option<Arc<dyn CatalogProvider>> {
+        self.catalogs.insert(name, catalog)
+    }
+
+    fn catalog_names(&self) -> Vec<String> {
+        self.catalogs
+            .iter()
+            .map(|entry| entry.key().clone())
+            .collect::<HashSet<_>>()
+            .into_iter()
+            .collect()
+    }
+
+    fn catalog(&self, name: &str) -> Option<Arc<dyn CatalogProvider>> {
+        self.catalogs
+            .get(name)
+            .map(|entry| Arc::clone(entry.value()))
+    }
+}
+
+/// A dynamic [`CatalogProvider`] that exposes the immediate child namespaces
+/// of a Lance namespace as database schemas.
+///
+/// The underlying namespace must be a three-level namespace. It is either explicitly
+/// registered via [`SessionBuilder::add_catalog`], or automatically created as part of
+/// the catalog hierarchy when [`SessionBuilder::with_root`] is used.
+/// Child namespaces are automatically loaded as [`LanceSchemaProvider`] instances.
+#[derive(Debug, Clone)]
+pub struct LanceCatalogProvider {
+    #[allow(dead_code)]
+    ns_level: NamespaceLevel,
+    /// Note: The values in this map may become stale over time, as there is currently
+    /// no mechanism to automatically refresh or invalidate cached schema providers.
+    schemas: DashMap<String, Arc<dyn SchemaProvider>>,
+}
+
+impl LanceCatalogProvider {
+    pub async fn try_new(namespace: NamespaceLevel) -> Result<Self> {
+        let schemas = DashMap::new();
+        for child_namespace in namespace.children().await? {
+            let schema_name = child_namespace.name().to_string();
+            let schema_provider = Arc::new(LanceSchemaProvider::try_new(child_namespace).await?);
+            schemas.insert(schema_name, schema_provider as Arc<dyn SchemaProvider>);
+        }
+
+        Ok(Self {
+            ns_level: namespace,
+            schemas,
+        })
+    }
+}
+
+impl CatalogProvider for LanceCatalogProvider {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn schema_names(&self) -> Vec<String> {
+        self.schemas
+            .iter()
+            .map(|entry| entry.key().clone())
+            .collect::<HashSet<_>>()
+            .into_iter()
+            .collect()
+    }
+
+    fn schema(&self, schema_name: &str) -> Option<Arc<dyn SchemaProvider>> {
+        self.schemas
+            .get(schema_name)
+            .map(|entry| Arc::clone(entry.value()))
+    }
+
+    fn register_schema(
+        &self,
+        name: &str,
+        schema: Arc<dyn SchemaProvider>,
+    ) -> Result<Option<Arc<dyn SchemaProvider>>> {
+        Ok(self.schemas.insert(name.to_string(), schema))
+    }
+}

rust/lance-namespace-datafusion/src/error.rs

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The Lance Authors
+
+use datafusion::error::DataFusionError;
+use lance::Error;
+
+/// Converts a lance error into a datafusion error.
+pub fn to_datafusion_error(error: Error) -> DataFusionError {
+    DataFusionError::External(error.into())
+}

rust/lance-namespace-datafusion/src/lib.rs

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The Lance Authors
+
+//! Lance integration between namespaces and Apache DataFusion catalogs.
+//!
+//! This crate provides adapters to expose Lance namespaces as
+//! DataFusion `CatalogProviderList`, `CatalogProvider`, and
+//! `SchemaProvider` implementations. It intentionally focuses on
+//! read-only catalog and schema mapping.
+
+pub mod catalog;
+pub mod error;
+pub mod namespace_level;
+pub mod schema;
+pub mod session_builder;
+
+pub use catalog::{LanceCatalogProvider, LanceCatalogProviderList};
+pub use namespace_level::NamespaceLevel;
+pub use schema::LanceSchemaProvider;
+pub use session_builder::SessionBuilder;