add BlockCursor::row_array_size

Changelog.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 2.2.0
+
+* Adds `BlockCursor::row_array_size`, in order to infer maximum batch size without unbinding the row set buffer first. This allows downstream `arrow-odbc` for a faster implementation then creating a double buffered concurrent stream of batches directly from a block cursor.
+
 ## 2.1.0
 
 It is now better possible to use `odbc-api` with multithreading in completly safe code.

odbc-api/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "odbc-api"
-version = "2.1.0"
+version = "2.2.0"
 authors = ["Markus Klein"]
 edition = "2021"
 license = "MIT"

odbc-api/src/cursor.rs

@@ -541,6 +541,13 @@ where
     }
 }
 
+impl<C,B> BlockCursor<C, B> where B: RowSetBuffer, C: AsStatementRef {
+    /// Maximum amount of rows fetched from the database in the next call to fetch.
+    pub fn row_array_size(&self) -> usize {
+        self.buffer.row_array_size()
+    }
+}
+
 impl<C, B> Drop for BlockCursor<C, B>
 where
     C: AsStatementRef,

odbc-api/tests/integration.rs

@@ -3880,6 +3880,30 @@ fn cursor_get_text_from_text(profile: &Profile) {
     assert_eq!("€".repeat(300), actual);
 }
 
+/// If we want to use two buffers alternating to fetch data (like in the concurrent use case in
+/// the arrow-odbc downstream crate) we may want to generate a second row set buffer from an
+/// existing one. For this it is useful if we can infer the capacity of the block cursor, without
+/// unbinding it first.
+#[test_case(MSSQL; "Microsoft SQL Server")]
+#[test_case(MARIADB; "Maria DB")]
+#[test_case(SQLITE_3; "SQLite 3")]
+#[test_case(POSTGRES; "PostgreSQL")]
+fn row_arrary_size_from_block_cursor(profile: &Profile) {
+    // Given a table
+    let table_name = table_name!();
+    let (conn, table) = profile.given(&table_name, &["INTEGER"]).unwrap();
+
+    // When
+    let capacity_used_to_create_buffer = 42;
+    let cursor = conn.execute(&table.sql_all_ordered_by_id(), ()).unwrap().unwrap();
+    let buffer = ColumnarAnyBuffer::from_descs(capacity_used_to_create_buffer, [BufferDesc::I32 { nullable: true }]);
+    let block_cursor = cursor.bind_buffer(buffer).unwrap();
+    let capacity_reported_by_block_cursor = block_cursor.row_array_size();
+
+    // Then
+    assert_eq!(capacity_used_to_create_buffer, capacity_reported_by_block_cursor);
+}
+
 #[test_case(MSSQL; "Microsoft SQL Server")]
 #[test_case(MARIADB; "Maria DB")]
 #[test_case(SQLITE_3; "SQLite 3")]

odbcsv/Cargo.toml

@@ -29,7 +29,7 @@ readme = "Readme.md"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-odbc-api = { version = "2.1.0", path = "../odbc-api" }
+odbc-api = { version = "2.2.0", path = "../odbc-api" }
 csv = "1.3.0"
 anyhow = "1.0.75"
 stderrlog = "0.5.4"