feat: add udf current_schema and current_schemas (#87)

* feat: add udf current_schema and current_schemas

* refactor: avoid hardcoded catalog name in library

* refactor: lint fix

Author: sunng87

datafusion-postgres-cli/src/main.rs

@@ -6,7 +6,7 @@ use datafusion::execution::options::{
     ArrowReadOptions, AvroReadOptions, CsvReadOptions, NdJsonReadOptions, ParquetReadOptions,
 };
 use datafusion::prelude::{SessionConfig, SessionContext};
-use datafusion_postgres::pg_catalog::PgCatalogSchemaProvider;
+use datafusion_postgres::pg_catalog::setup_pg_catalog;
 use datafusion_postgres::{serve, ServerOptions}; // Assuming the crate name is `datafusion_postgres`
 use structopt::StructOpt;
 
@@ -171,11 +171,7 @@ async fn setup_session_context(
     }
 
     // Register pg_catalog
-    let pg_catalog = PgCatalogSchemaProvider::new(session_context.state().catalog_list().clone());
-    session_context
-        .catalog("datafusion")
-        .unwrap()
-        .register_schema("pg_catalog", Arc::new(pg_catalog))?;
+    setup_pg_catalog(session_context, "datafusion")?;
 
     Ok(())
 }

datafusion-postgres/src/pg_catalog.rs

@@ -2,16 +2,20 @@ use std::sync::Arc;
 
 use async_trait::async_trait;
 use datafusion::arrow::array::{
-    ArrayRef, BooleanArray, Float64Array, Int16Array, Int32Array, RecordBatch, StringArray,
+    as_boolean_array, ArrayRef, BooleanArray, Float64Array, Int16Array, Int32Array, RecordBatch,
+    StringArray, StringBuilder,
 };
 use datafusion::arrow::datatypes::{DataType, Field, Schema, SchemaRef};
 use datafusion::catalog::streaming::StreamingTable;
 use datafusion::catalog::{CatalogProviderList, MemTable, SchemaProvider};
+use datafusion::common::utils::SingleRowListArrayBuilder;
 use datafusion::datasource::TableProvider;
-use datafusion::error::Result;
+use datafusion::error::{DataFusionError, Result};
 use datafusion::execution::{SendableRecordBatchStream, TaskContext};
+use datafusion::logical_expr::{ColumnarValue, ScalarUDF, Volatility};
 use datafusion::physical_plan::stream::RecordBatchStreamAdapter;
 use datafusion::physical_plan::streaming::PartitionStream;
+use datafusion::prelude::{create_udf, SessionContext};
 
 const PG_CATALOG_TABLE_PG_TYPE: &str = "pg_type";
 const PG_CATALOG_TABLE_PG_CLASS: &str = "pg_class";
@@ -595,3 +599,77 @@ impl PartitionStream for PgDatabaseTable {
         ))
     }
 }
+
+pub fn create_current_schemas_udf() -> ScalarUDF {
+    // Define the function implementation
+    let func = move |args: &[ColumnarValue]| {
+        let args = ColumnarValue::values_to_arrays(args)?;
+        let input = as_boolean_array(&args[0]);
+
+        // Create a UTF8 array with a single value
+        let mut values = vec!["public"];
+        // include implicit schemas
+        if input.value(0) {
+            values.push("information_schema");
+            values.push("pg_catalog");
+        }
+
+        let list_array = SingleRowListArrayBuilder::new(Arc::new(StringArray::from(values)));
+
+        let array: ArrayRef = Arc::new(list_array.build_list_array());
+
+        Ok(ColumnarValue::Array(array))
+    };
+
+    // Wrap the implementation in a scalar function
+    create_udf(
+        "current_schemas",
+        vec![DataType::Boolean],
+        DataType::List(Arc::new(Field::new("schema", DataType::Utf8, false))),
+        Volatility::Immutable,
+        Arc::new(func),
+    )
+}
+
+pub fn create_current_schema_udf() -> ScalarUDF {
+    // Define the function implementation
+    let func = move |_args: &[ColumnarValue]| {
+        // Create a UTF8 array with a single value
+        let mut builder = StringBuilder::new();
+        builder.append_value("public");
+        let array: ArrayRef = Arc::new(builder.finish());
+
+        Ok(ColumnarValue::Array(array))
+    };
+
+    // Wrap the implementation in a scalar function
+    create_udf(
+        "current_schema",
+        vec![],
+        DataType::Utf8,
+        Volatility::Immutable,
+        Arc::new(func),
+    )
+}
+
+/// Install pg_catalog and postgres UDFs to current `SessionContext`
+pub fn setup_pg_catalog(
+    session_context: &SessionContext,
+    catalog_name: &str,
+) -> Result<(), Box<DataFusionError>> {
+    let pg_catalog = PgCatalogSchemaProvider::new(session_context.state().catalog_list().clone());
+    session_context
+        .catalog(catalog_name)
+        .ok_or_else(|| {
+            DataFusionError::Configuration(format!(
+                "Catalog not found when registering pg_catalog: {}",
+                catalog_name
+            ))
+        })?
+        .register_schema("pg_catalog", Arc::new(pg_catalog))?;
+
+    session_context.register_udf(create_current_schema_udf());
+    session_context.register_udf(create_current_schemas_udf());
+
+    Ok(())
+}