feat: add placeholder table/functions for pg_description queries (#116)

Author: sunng87

datafusion-postgres/src/pg_catalog.rs

@@ -30,6 +30,7 @@ const PG_CATALOG_TABLE_PG_DATABASE: &str = "pg_database";
 const PG_CATALOG_TABLE_PG_AM: &str = "pg_am";
 const PG_CATALOG_TABLE_PG_RANGE: &str = "pg_range";
 const PG_CATALOG_TABLE_PG_ENUM: &str = "pg_enum";
+const PG_CATALOG_TABLE_PG_DESCRIPTION: &str = "pg_description";
 
 /// Determine PostgreSQL table type (relkind) from DataFusion TableProvider
 fn get_table_type(table: &Arc<dyn TableProvider>) -> &'static str {
@@ -72,6 +73,7 @@ pub const PG_CATALOG_TABLES: &[&str] = &[
     PG_CATALOG_TABLE_PG_AM,
     PG_CATALOG_TABLE_PG_RANGE,
     PG_CATALOG_TABLE_PG_ENUM,
+    PG_CATALOG_TABLE_PG_DESCRIPTION,
 ];
 
 // Data structure to hold pg_type table data
@@ -281,6 +283,7 @@ impl SchemaProvider for PgCatalogSchemaProvider {
             PG_CATALOG_TABLE_PG_PROC => Ok(Some(self.create_pg_proc_table())),
             PG_CATALOG_TABLE_PG_RANGE => Ok(Some(self.create_pg_range_table())),
             PG_CATALOG_TABLE_PG_ENUM => Ok(Some(self.create_pg_enum_table())),
+            PG_CATALOG_TABLE_PG_DESCRIPTION => Ok(Some(self.create_pg_description_table())),
             _ => Ok(None),
         }
     }
@@ -782,6 +785,18 @@ impl PgCatalogSchemaProvider {
         Arc::new(provider)
     }
 
+    /// Create a mock empty table for pg_description
+    fn create_pg_description_table(&self) -> Arc<dyn TableProvider> {
+        let schema = Arc::new(Schema::new(vec![
+            Field::new("objoid", DataType::Int32, false),   // Oid
+            Field::new("classoid", DataType::Int32, false), // Oid of the obj class
+            Field::new("objsubid", DataType::Int32, false), // subid
+            Field::new("description", DataType::Utf8, false),
+        ]));
+        let provider = MemTable::try_new(schema, vec![vec![]]).unwrap();
+        Arc::new(provider)
+    }
+
     /// Create a populated pg_proc table with standard PostgreSQL functions
     fn create_pg_proc_table(&self) -> Arc<dyn TableProvider> {
         // Define complete schema for pg_proc (matching PostgreSQL)
@@ -1927,13 +1942,16 @@ pub fn create_has_table_privilege_3param_udf() -> ScalarUDF {
     // Define the function implementation for 3-parameter version
     let func = move |args: &[ColumnarValue]| {
         let args = ColumnarValue::values_to_arrays(args)?;
-        let _user = &args[0]; // User (can be name or OID)
+        let user = &args[0]; // User (can be name or OID)
         let _table = &args[1]; // Table (can be name or OID)
         let _privilege = &args[2]; // Privilege type (SELECT, INSERT, etc.)
 
         // For now, always return true (full access)
-        let mut builder = BooleanArray::builder(1);
-        builder.append_value(true);
+        let mut builder = BooleanArray::builder(user.len());
+        for _ in 0..user.len() {
+            builder.append_value(true);
+        }
+
         let array: ArrayRef = Arc::new(builder.finish());
 
         Ok(ColumnarValue::Array(array))
@@ -1953,12 +1971,14 @@ pub fn create_has_table_privilege_2param_udf() -> ScalarUDF {
     // Define the function implementation for 2-parameter version (current user, table, privilege)
     let func = move |args: &[ColumnarValue]| {
         let args = ColumnarValue::values_to_arrays(args)?;
-        let _table = &args[0]; // Table (can be name or OID)
+        let table = &args[0]; // Table (can be name or OID)
         let _privilege = &args[1]; // Privilege type (SELECT, INSERT, etc.)
 
         // For now, always return true (full access for current user)
-        let mut builder = BooleanArray::builder(1);
-        builder.append_value(true);
+        let mut builder = BooleanArray::builder(table.len());
+        for _ in 0..table.len() {
+            builder.append_value(true);
+        }
         let array: ArrayRef = Arc::new(builder.finish());
 
         Ok(ColumnarValue::Array(array))
@@ -1974,6 +1994,32 @@ pub fn create_has_table_privilege_2param_udf() -> ScalarUDF {
     )
 }
 
+pub fn create_format_type_udf() -> ScalarUDF {
+    let func = move |args: &[ColumnarValue]| {
+        let args = ColumnarValue::values_to_arrays(args)?;
+        let type_oids = &args[0]; // Table (can be name or OID)
+        let _type_mods = &args[1]; // Privilege type (SELECT, INSERT, etc.)
+
+        // For now, always return true (full access for current user)
+        let mut builder = StringBuilder::new();
+        for _ in 0..type_oids.len() {
+            builder.append_value("???");
+        }
+
+        let array: ArrayRef = Arc::new(builder.finish());
+
+        Ok(ColumnarValue::Array(array))
+    };
+
+    create_udf(
+        "format_type",
+        vec![DataType::Int32, DataType::Int32],
+        DataType::Utf8,
+        Volatility::Stable,
+        Arc::new(func),
+    )
+}
+
 /// Install pg_catalog and postgres UDFs to current `SessionContext`
 pub fn setup_pg_catalog(
     session_context: &SessionContext,
@@ -1995,6 +2041,7 @@ pub fn setup_pg_catalog(
     session_context.register_udf(create_pg_get_userbyid_udf());
     session_context.register_udf(create_has_table_privilege_2param_udf());
     session_context.register_udf(create_pg_table_is_visible());
+    session_context.register_udf(create_format_type_udf());
 
     Ok(())
 }