Avoid DDL when checking for versions table golang-migrate#134

bodyguard-ai · Jan 6, 2017 · da6c505 · da6c505
1 parent 966ba84
commit da6c505
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Showing 2 changed files with 13 additions and 0 deletions.
diff --git a/driver/postgres/postgres.go b/driver/postgres/postgres.go
@@ -43,6 +43,14 @@ func (driver *Driver) Close() error {
 }
 
 func (driver *Driver) ensureVersionTableExists() error {
+	r := driver.db.QueryRow("SELECT count(*) FROM information_schema.tables WHERE table_name = $1;", tableName)
+	c := 0
+	if err := r.Scan(&c); err != nil {
+		return err
+	}
+	if c > 0 {
+		return nil
+	}
 	if _, err := driver.db.Exec("CREATE TABLE IF NOT EXISTS " + tableName + " (version int not null primary key);"); err != nil {
 		return err
 	}

diff --git a/driver/postgres/postgres_test.go b/driver/postgres/postgres_test.go
@@ -37,6 +37,11 @@ func TestMigrate(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// testing idempotency: second call should be a no-op, since table already exists
+	if err := d.Initialize(driverUrl); err != nil {
+		t.Fatal(err)
+	}
+
 	files := []file.File{
 		{
 			Path:      "/foobar",