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converter.go
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converter.go
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package sqlutil
import (
"database/sql"
"fmt"
"reflect"
"time"
"github.com/grafana/grafana-plugin-sdk-go/data"
)
// FrameConverter defines how to convert the scanned value into a value that can be put into a dataframe (OutputFieldType)
type FrameConverter struct {
// FieldType is the type that is created for the dataframe field.
// The returned value from `ConverterFunc` should match this type, otherwise the data package will panic.
FieldType data.FieldType
// ConverterFunc defines how to convert the scanned `InputScanType` to the supplied `FieldType`.
// `in` is always supplied as a pointer, as it is scanned as a pointer, even if `InputScanType` is not a pointer.
// For example, if `InputScanType` is `string`, then `in` is `*string`
ConverterFunc func(in interface{}) (interface{}, error)
}
// StringConverter can be used to store types not supported by
// a Frame into a *string. When scanning, if a SQL's row's InputScanType's Kind
// and InputScanKind match that returned by the sql response, then the
// conversion func will be run on the row.
// Note, a Converter should be favored over a StringConverter as not all SQL rows can be scanned into a string.
// This type is only here for backwards compatibility.
type StringConverter struct {
// Name is an optional property that can be used to identify a converter
Name string
InputScanKind reflect.Kind // reflect.Type might better or worse option?
InputTypeName string
// Conversion func may be nil to do no additional operations on the string conversion.
ConversionFunc func(in *string) (*string, error)
// If the Replacer is not nil, the replacement will be performed.
Replacer *StringFieldReplacer
}
// Note: StringConverter is perhaps better understood as []byte. However, currently
// the Vector type ([][]byte) is not supported. https://github.com/grafana/grafana-plugin-sdk-go/issues/57
// StringFieldReplacer is used to replace a *string Field in a Frame. The type
// returned by the ReplaceFunc must match the type of elements of VectorType.
// Both properties must be non-nil.
// Note, a Converter should be favored over a StringConverter as not all SQL rows can be scanned into a string.
// This type is only here for backwards compatibility.
type StringFieldReplacer struct {
OutputFieldType data.FieldType
ReplaceFunc func(in *string) (interface{}, error)
}
// ToConverter turns this StringConverter into a Converter, using the ScanType of string
func (s StringConverter) ToConverter() Converter {
return Converter{
Name: s.Name,
InputScanType: reflect.TypeOf(sql.NullString{}),
InputTypeName: s.InputTypeName,
FrameConverter: StringFrameConverter(s),
}
}
// StringFrameConverter creates a FrameConverter from a StringConverter
func StringFrameConverter(s StringConverter) FrameConverter {
f := data.FieldTypeNullableString
if s.Replacer != nil {
f = s.Replacer.OutputFieldType
}
return FrameConverter{
FieldType: f,
ConverterFunc: func(in interface{}) (interface{}, error) {
ns := in.(*sql.NullString)
if !ns.Valid {
return nil, nil
}
v := &ns.String
if s.ConversionFunc != nil {
converted, err := s.ConversionFunc(v)
if err != nil {
return nil, err
}
v = converted
}
if s.Replacer.ReplaceFunc != nil {
return s.Replacer.ReplaceFunc(v)
}
return v, nil
},
}
}
// ToConverters creates a slice of Converters from a slice of StringConverters
func ToConverters(s ...StringConverter) []Converter {
n := make([]Converter, len(s))
for i, v := range s {
n[i] = v.ToConverter()
}
return n
}
// Converter is used to convert known types returned in sql.Row to a type usable in a dataframe.
type Converter struct {
// Name is the name of the converter that is used to distinguish them when debugging or parsing log output
Name string
// InputScanType is the type that is used when (*sql.Rows).Scan(...) is called.
// Some drivers require certain data types to be used when scanning data from sql rows, and this type should reflect that.
InputScanType reflect.Type
// InputTypeName is the case-sensitive name that must match the type that this converter matches
InputTypeName string
// FrameConverter defines how to convert the scanned value into a value that can be put into a dataframe
FrameConverter FrameConverter
}
// DefaultConverterFunc assumes that the scanned value, in, is already a type that can be put into a dataframe.
func DefaultConverterFunc(t reflect.Type) func(in interface{}) (interface{}, error) {
return func(in interface{}) (interface{}, error) {
inType := reflect.TypeOf(in)
if inType == reflect.PtrTo(t) {
n := reflect.ValueOf(in)
return n.Elem().Interface(), nil
}
return in, nil
}
}
// NewDefaultConverter creates a Converter that assumes that the value is scannable into a String, and placed into the dataframe as a nullable string.
func NewDefaultConverter(name string, nullable bool, t reflect.Type) Converter {
slice := reflect.MakeSlice(reflect.SliceOf(t), 0, 0).Interface()
if !data.ValidFieldType(slice) {
return Converter{
Name: fmt.Sprintf("[%s] String converter", t),
InputScanType: reflect.TypeOf(sql.NullString{}),
InputTypeName: name,
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableString,
ConverterFunc: func(in interface{}) (interface{}, error) {
v := in.(*sql.NullString)
if !v.Valid {
return (*string)(nil), nil
}
f := v.String
return &f, nil
},
},
}
}
v := reflect.New(t)
var fieldType data.FieldType
if v.Type() == reflect.PtrTo(t) {
v = v.Elem()
fieldType = data.FieldTypeFor(v.Interface())
} else {
fieldType = data.FieldTypeFor(v.Interface()).NullableType()
}
if nullable {
if converter, ok := NullConverters[t]; ok {
return converter
}
}
return Converter{
Name: fmt.Sprintf("Default converter for %s", name),
InputScanType: t,
InputTypeName: name,
FrameConverter: FrameConverter{
FieldType: fieldType,
ConverterFunc: DefaultConverterFunc(t),
},
}
}
var (
// NullStringConverter creates a *string using the scan type of `sql.NullString`
NullStringConverter = Converter{
Name: "nullable string converter",
InputScanType: reflect.TypeOf(sql.NullString{}),
InputTypeName: "STRING",
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableString,
ConverterFunc: func(n interface{}) (interface{}, error) {
v := n.(*sql.NullString)
if !v.Valid {
return (*string)(nil), nil
}
f := v.String
return &f, nil
},
},
}
// NullDecimalConverter creates a *float64 using the scan type of `sql.NullFloat64`
NullDecimalConverter = Converter{
Name: "NULLABLE decimal converter",
InputScanType: reflect.TypeOf(sql.NullFloat64{}),
InputTypeName: "DOUBLE",
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableFloat64,
ConverterFunc: func(n interface{}) (interface{}, error) {
v := n.(*sql.NullFloat64)
if !v.Valid {
return (*float64)(nil), nil
}
f := v.Float64
return &f, nil
},
},
}
// NullInt64Converter creates a *int64 using the scan type of `sql.NullInt64`
NullInt64Converter = Converter{
Name: "NULLABLE int64 converter",
InputScanType: reflect.TypeOf(sql.NullInt64{}),
InputTypeName: "INTEGER",
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableInt64,
ConverterFunc: func(n interface{}) (interface{}, error) {
v := n.(*sql.NullInt64)
if !v.Valid {
return (*int64)(nil), nil
}
f := v.Int64
return &f, nil
},
},
}
// NullInt32Converter creates a *int32 using the scan type of `sql.NullInt32`
NullInt32Converter = Converter{
Name: "NULLABLE int32 converter",
InputScanType: reflect.TypeOf(sql.NullInt32{}),
InputTypeName: "INTEGER",
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableInt32,
ConverterFunc: func(n interface{}) (interface{}, error) {
v := n.(*sql.NullInt32)
if !v.Valid {
return (*int32)(nil), nil
}
f := v.Int32
return &f, nil
},
},
}
// NullTimeConverter creates a *time.time using the scan type of `sql.NullTime`
NullTimeConverter = Converter{
Name: "NULLABLE time.Time converter",
InputScanType: reflect.TypeOf(sql.NullTime{}),
InputTypeName: "TIMESTAMP",
FrameConverter: FrameConverter{
FieldType: data.FieldTypeNullableTime,
ConverterFunc: func(n interface{}) (interface{}, error) {
v := n.(*sql.NullTime)
if !v.Valid {
return (*time.Time)(nil), nil
}
f := v.Time
return &f, nil
},
},
}
)
// NullConverters is a map of data type names (from reflect.TypeOf(...).String()) to converters
// Converters supplied here are used as defaults for fields that do not have a supplied Converter
var NullConverters = map[reflect.Type]Converter{
reflect.TypeOf(float64(0)): NullDecimalConverter,
reflect.TypeOf(int64(0)): NullInt64Converter,
reflect.TypeOf(int32(0)): NullInt32Converter,
reflect.TypeOf(""): NullStringConverter,
reflect.TypeOf(time.Time{}): NullTimeConverter,
}