Add more ColumnType support

messages.go

@@ -1,14 +1,19 @@
 package pgx
 
 import (
+	"math"
+	"reflect"
+	"time"
+
 	"github.com/jackc/pgx/pgio"
 	"github.com/jackc/pgx/pgtype"
 )
 
 const (
-	copyData = 'd'
-	copyFail = 'f'
-	copyDone = 'c'
+	copyData      = 'd'
+	copyFail      = 'f'
+	copyDone      = 'c'
+	varHeaderSize = 4
 )
 
 type FieldDescription struct {
@@ -22,6 +27,52 @@ type FieldDescription struct {
 	FormatCode      int16
 }
 
+func (fd FieldDescription) Length() (int64, bool) {
+	switch fd.DataType {
+	case pgtype.TextOID, pgtype.ByteaOID:
+		return math.MaxInt64, true
+	case pgtype.VarcharOID:
+		return int64(fd.Modifier - varHeaderSize), true
+	default:
+		return 0, false
+	}
+}
+
+func (fd FieldDescription) PrecisionScale() (precision, scale int64, ok bool) {
+	switch fd.DataType {
+	case pgtype.NumericOID:
+		mod := fd.Modifier - varHeaderSize
+		precision = int64((mod >> 16) & 0xffff)
+		scale = int64(mod & 0xffff)
+		return precision, scale, true
+	default:
+		return 0, 0, false
+	}
+}
+
+func (fd FieldDescription) Type() reflect.Type {
+	switch fd.DataType {
+	case pgtype.Int8OID:
+		return reflect.TypeOf(int64(0))
+	case pgtype.Int4OID:
+		return reflect.TypeOf(int32(0))
+	case pgtype.Int2OID:
+		return reflect.TypeOf(int16(0))
+	case pgtype.VarcharOID, pgtype.TextOID:
+		return reflect.TypeOf("")
+	case pgtype.BoolOID:
+		return reflect.TypeOf(false)
+	case pgtype.NumericOID:
+		return reflect.TypeOf(float64(0))
+	case pgtype.DateOID, pgtype.TimestampOID, pgtype.TimestamptzOID:
+		return reflect.TypeOf(time.Time{})
+	case pgtype.ByteaOID:
+		return reflect.TypeOf([]byte(nil))
+	default:
+		return reflect.TypeOf(new(interface{})).Elem()
+	}
+}
+
 // PgError represents an error reported by the PostgreSQL server. See
 // http://www.postgresql.org/docs/9.3/static/protocol-error-fields.html for
 // detailed field description.

pgtype/pgtype.go

@@ -46,6 +46,7 @@ const (
 	DateArrayOID        = 1182
 	TimestamptzOID      = 1184
 	TimestamptzArrayOID = 1185
+	NumericOID          = 1700
 	RecordOID           = 2249
 	UUIDOID             = 2950
 	JSONBOID            = 3802

stdlib/sql.go

@@ -70,6 +70,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"reflect"
 	"strings"
 	"sync"
 
@@ -415,10 +416,29 @@ func (r *Rows) Columns() []string {
 	return names
 }
 
+// ColumnTypeDatabaseTypeName return the database system type name.
 func (r *Rows) ColumnTypeDatabaseTypeName(index int) string {
 	return strings.ToUpper(r.rows.FieldDescriptions()[index].DataTypeName)
 }
 
+// ColumnTypeLength returns the length of the column type if the column is a
+// variable length type. If the column is not a variable length type ok
+// should return false.
+func (r *Rows) ColumnTypeLength(index int) (int64, bool) {
+	return r.rows.FieldDescriptions()[index].Length()
+}
+
+// ColumnTypePrecisionScale should return the precision and scale for decimal
+// types. If not applicable, ok should be false.
+func (r *Rows) ColumnTypePrecisionScale(index int) (precision, scale int64, ok bool) {
+	return r.rows.FieldDescriptions()[index].PrecisionScale()
+}
+
+// ColumnTypeScanType returns the value type that can be used to scan types into.
+func (r *Rows) ColumnTypeScanType(index int) reflect.Type {
+	return r.rows.FieldDescriptions()[index].Type()
+}
+
 func (r *Rows) Close() error {
 	r.rows.Close()
 	return nil

stdlib/sql_test.go

@@ -5,6 +5,8 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"math"
+	"reflect"
 	"testing"
 	"time"
 
@@ -1258,3 +1260,128 @@ func TestStmtQueryContextCancel(t *testing.T) {
 		t.Errorf("mock server err: %v", err)
 	}
 }
+
+func TestRowsColumnTypes(t *testing.T) {
+	columnTypesTests := []struct {
+		Name     string
+		TypeName string
+		Length   struct {
+			Len int64
+			OK  bool
+		}
+		DecimalSize struct {
+			Precision int64
+			Scale     int64
+			OK        bool
+		}
+		ScanType reflect.Type
+	}{
+		{
+			Name:     "a",
+			TypeName: "INT4",
+			Length: struct {
+				Len int64
+				OK  bool
+			}{
+				Len: 0,
+				OK:  false,
+			},
+			DecimalSize: struct {
+				Precision int64
+				Scale     int64
+				OK        bool
+			}{
+				Precision: 0,
+				Scale:     0,
+				OK:        false,
+			},
+			ScanType: reflect.TypeOf(int32(0)),
+		}, {
+			Name:     "bar",
+			TypeName: "TEXT",
+			Length: struct {
+				Len int64
+				OK  bool
+			}{
+				Len: math.MaxInt64,
+				OK:  true,
+			},
+			DecimalSize: struct {
+				Precision int64
+				Scale     int64
+				OK        bool
+			}{
+				Precision: 0,
+				Scale:     0,
+				OK:        false,
+			},
+			ScanType: reflect.TypeOf(""),
+		}, {
+			Name:     "dec",
+			TypeName: "NUMERIC",
+			Length: struct {
+				Len int64
+				OK  bool
+			}{
+				Len: 0,
+				OK:  false,
+			},
+			DecimalSize: struct {
+				Precision int64
+				Scale     int64
+				OK        bool
+			}{
+				Precision: 9,
+				Scale:     2,
+				OK:        true,
+			},
+			ScanType: reflect.TypeOf(float64(0)),
+		},
+	}
+
+	db := openDB(t)
+	defer closeDB(t, db)
+
+	rows, err := db.Query("SELECT 1 AS a, text 'bar' AS bar, 1.28::numeric(9, 2) AS dec")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	columns, err := rows.ColumnTypes()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(columns) != 3 {
+		t.Errorf("expected 3 columns found %d", len(columns))
+	}
+
+	for i, tt := range columnTypesTests {
+		c := columns[i]
+		if c.Name() != tt.Name {
+			t.Errorf("(%d) got: %s, want: %s", i, c.Name(), tt.Name)
+		}
+		if c.DatabaseTypeName() != tt.TypeName {
+			t.Errorf("(%d) got: %s, want: %s", i, c.DatabaseTypeName(), tt.TypeName)
+		}
+		l, ok := c.Length()
+		if l != tt.Length.Len {
+			t.Errorf("(%d) got: %d, want: %d", i, l, tt.Length.Len)
+		}
+		if ok != tt.Length.OK {
+			t.Errorf("(%d) got: %t, want: %t", i, ok, tt.Length.OK)
+		}
+		p, s, ok := c.DecimalSize()
+		if p != tt.DecimalSize.Precision {
+			t.Errorf("(%d) got: %d, want: %d", i, p, tt.DecimalSize.Precision)
+		}
+		if s != tt.DecimalSize.Scale {
+			t.Errorf("(%d) got: %d, want: %d", i, s, tt.DecimalSize.Scale)
+		}
+		if ok != tt.DecimalSize.OK {
+			t.Errorf("(%d) got: %t, want: %t", i, ok, tt.DecimalSize.OK)
+		}
+		if c.ScanType() != tt.ScanType {
+			t.Errorf("(%d) got: %v, want: %v", i, c.ScanType(), tt.ScanType)
+		}
+	}
+}