source: code/trunk/vendor/github.com/lib/pq/rows.go@ 822

package pq

import (
        "math"
        "reflect"
        "time"

        "github.com/lib/pq/oid"
)

const headerSize = 4

type fieldDesc struct {
        // The object ID of the data type.
        OID oid.Oid
        // The data type size (see pg_type.typlen).
        // Note that negative values denote variable-width types.
        Len int
        // The type modifier (see pg_attribute.atttypmod).
        // The meaning of the modifier is type-specific.
        Mod int
}

func (fd fieldDesc) Type() reflect.Type {
        switch fd.OID {
        case oid.T_int8:
                return reflect.TypeOf(int64(0))
        case oid.T_int4:
                return reflect.TypeOf(int32(0))
        case oid.T_int2:
                return reflect.TypeOf(int16(0))
        case oid.T_varchar, oid.T_text:
                return reflect.TypeOf("")
        case oid.T_bool:
                return reflect.TypeOf(false)
        case oid.T_date, oid.T_time, oid.T_timetz, oid.T_timestamp, oid.T_timestamptz:
                return reflect.TypeOf(time.Time{})
        case oid.T_bytea:
                return reflect.TypeOf([]byte(nil))
        default:
                return reflect.TypeOf(new(interface{})).Elem()
        }
}

func (fd fieldDesc) Name() string {
        return oid.TypeName[fd.OID]
}

func (fd fieldDesc) Length() (length int64, ok bool) {
        switch fd.OID {
        case oid.T_text, oid.T_bytea:
                return math.MaxInt64, true
        case oid.T_varchar, oid.T_bpchar:
                return int64(fd.Mod - headerSize), true
        default:
                return 0, false
        }
}

func (fd fieldDesc) PrecisionScale() (precision, scale int64, ok bool) {
        switch fd.OID {
        case oid.T_numeric, oid.T__numeric:
                mod := fd.Mod - headerSize
                precision = int64((mod >> 16) & 0xffff)
                scale = int64(mod & 0xffff)
                return precision, scale, true
        default:
                return 0, 0, false
        }
}

// ColumnTypeScanType returns the value type that can be used to scan types into.
func (rs *rows) ColumnTypeScanType(index int) reflect.Type {
        return rs.colTyps[index].Type()
}

// ColumnTypeDatabaseTypeName return the database system type name.
func (rs *rows) ColumnTypeDatabaseTypeName(index int) string {
        return rs.colTyps[index].Name()
}

// 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 (rs *rows) ColumnTypeLength(index int) (length int64, ok bool) {
        return rs.colTyps[index].Length()
}

// ColumnTypePrecisionScale should return the precision and scale for decimal
// types. If not applicable, ok should be false.
func (rs *rows) ColumnTypePrecisionScale(index int) (precision, scale int64, ok bool) {
        return rs.colTyps[index].PrecisionScale()
}