Add WithConnection to Postgres similar to MySQL.

database/postgres/postgres.go

@@ -7,7 +7,6 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
-	"go.uber.org/atomic"
 	"io"
 	"io/ioutil"
 	nurl "net/url"
@@ -16,10 +15,12 @@ import (
 	"strings"
 	"time"
 
+	"go.uber.org/atomic"
+
 	"github.com/golang-migrate/migrate/v4"
 	"github.com/golang-migrate/migrate/v4/database"
 	"github.com/golang-migrate/migrate/v4/database/multistmt"
-	multierror "github.com/hashicorp/go-multierror"
+	"github.com/hashicorp/go-multierror"
 	"github.com/lib/pq"
 )
 
@@ -65,19 +66,19 @@ type Postgres struct {
 	config *Config
 }
 
-func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
+func WithConnection(ctx context.Context, conn *sql.Conn, config *Config) (*Postgres, error) {
 	if config == nil {
 		return nil, ErrNilConfig
 	}
 
-	if err := instance.Ping(); err != nil {
+	if err := conn.PingContext(ctx); err != nil {
 		return nil, err
 	}
 
 	if config.DatabaseName == "" {
 		query := `SELECT CURRENT_DATABASE()`
 		var databaseName string
-		if err := instance.QueryRow(query).Scan(&databaseName); err != nil {
+		if err := conn.QueryRowContext(ctx, query).Scan(&databaseName); err != nil {
 			return nil, &database.Error{OrigErr: err, Query: []byte(query)}
 		}
 
@@ -91,7 +92,7 @@ func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
 	if config.SchemaName == "" {
 		query := `SELECT CURRENT_SCHEMA()`
 		var schemaName string
-		if err := instance.QueryRow(query).Scan(&schemaName); err != nil {
+		if err := conn.QueryRowContext(ctx, query).Scan(&schemaName); err != nil {
 			return nil, &database.Error{OrigErr: err, Query: []byte(query)}
 		}
 
@@ -119,15 +120,8 @@ func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
 		}
 	}
 
-	conn, err := instance.Conn(context.Background())
-
-	if err != nil {
-		return nil, err
-	}
-
 	px := &Postgres{
 		conn:   conn,
-		db:     instance,
 		config: config,
 	}
 
@@ -138,6 +132,26 @@ func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
 	return px, nil
 }
 
+func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
+	ctx := context.Background()
+
+	if err := instance.Ping(); err != nil {
+		return nil, err
+	}
+
+	conn, err := instance.Conn(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	px, err := WithConnection(ctx, conn, config)
+	if err != nil {
+		return nil, err
+	}
+	px.db = instance
+	return px, nil
+}
+
 func (p *Postgres) Open(url string) (database.Driver, error) {
 	purl, err := nurl.Parse(url)
 	if err != nil {
@@ -207,7 +221,11 @@ func (p *Postgres) Open(url string) (database.Driver, error) {
 
 func (p *Postgres) Close() error {
 	connErr := p.conn.Close()
-	dbErr := p.db.Close()
+	var dbErr error
+	if p.db != nil {
+		dbErr = p.db.Close()
+	}
+
 	if connErr != nil || dbErr != nil {
 		return fmt.Errorf("conn: %v, db: %v", connErr, dbErr)
 	}

database/postgres/postgres_test.go

@@ -684,6 +684,44 @@ func TestWithInstance_Concurrent(t *testing.T) {
 		}
 	})
 }
+
+func TestWithConnection(t *testing.T) {
+	dktesting.ParallelTest(t, specs, func(t *testing.T, c dktest.ContainerInfo) {
+		ip, port, err := c.FirstPort()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		db, err := sql.Open("postgres", pgConnectionString(ip, port))
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer func() {
+			if err := db.Close(); err != nil {
+				t.Error(err)
+			}
+		}()
+
+		ctx := context.Background()
+		conn, err := db.Conn(ctx)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		p, err := WithConnection(ctx, conn, &Config{})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		defer func() {
+			if err := p.Close(); err != nil {
+				t.Error(err)
+			}
+		}()
+		dt.Test(t, p, []byte("SELECT 1"))
+	})
+}
+
 func Test_computeLineFromPos(t *testing.T) {
 	testcases := []struct {
 		pos      int