entc/gen: generate sql builders with dialect option

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/130

Reviewed By: alexsn

Differential Revision: D18164397

fbshipit-source-id: 2858d69d3ff85c06b51382c01c3d4369ee2c3bdb

entc/gen/template/dialect/sql/globals.tmpl

@@ -0,0 +1,40 @@
+{{/*
+Copyright 2019-present Facebook Inc. All rights reserved.
+This source code is licensed under the Apache 2.0 license found
+in the LICENSE file in the root directory of this source tree.
+*/}}
+
+{{/* custom globals and helpers for sql dialects */}}
+{{ define "dialect/sql/globals" }}
+// insertLastID invokes the insert query on the transaction and returns the LastInsertID.
+func insertLastID(ctx context.Context, tx dialect.Tx, insert *sql.InsertBuilder) (int64, error) {
+	query, args := insert.Query()
+	// PostgreSQL does not support the LastInsertId() method of sql.Result
+	// on Exec, and should be extracted manually using the `RETURNING` clause.
+	if insert.Dialect() == dialect.Postgres {
+		rows := &sql.Rows{}
+		if err := tx.Query(ctx, query, args, rows); err != nil {
+			return 0, err
+		}
+		defer rows.Close()
+		if !rows.Next() {
+			return 0, fmt.Errorf("no rows found for query: %v", query)
+		}
+		var id int64
+		if err := rows.Scan(&id); err != nil {
+			return 0, err
+		}
+		return id, nil
+	}
+	// MySQL, SQLite, etc.
+	var res sql.Result
+	if err := tx.Exec(ctx, query, args, &res); err != nil {
+		return 0, err
+	}
+	id, err := res.LastInsertId()
+	if err != nil {
+		return 0, err
+	}
+	return id, nil
+}
+{{ end }}