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query.go
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query.go
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package query
import (
"reflect"
"strings"
"github.com/pkg/errors"
)
// Query represents a query to extract the element from a value.
type Query struct {
extractors []Extractor
caseInsensitive bool
structTags []string
customExtractFuncs []func(ExtractFunc) ExtractFunc
customStructFieldNameGetter func(f reflect.StructField) string
customIsInlineFuncs []func(reflect.StructField) bool
hasExplicitRoot bool
}
// New returns a new query.
func New(opts ...Option) *Query {
q := &Query{}
for _, opt := range opts {
opt(q)
}
return q
}
// Append appends extractor to q and returns updated q.
func (q Query) Append(es ...Extractor) *Query {
extractors := make([]Extractor, 0, len(q.extractors)+len(es))
extractors = append(extractors, q.extractors...)
extractors = append(extractors, es...)
q.extractors = extractors
return &q
}
// Root marks that q has an explicit root operator $.
func (q Query) Root() *Query {
q.hasExplicitRoot = true
return &q
}
// Key is shorthand method to create Key and appends it.
func (q Query) Key(k string) *Query {
return q.Append(&Key{
key: k,
caseInsensitive: q.caseInsensitive,
structTags: q.structTags,
customExtractFuncs: q.customExtractFuncs,
fieldNameGetter: q.customStructFieldNameGetter,
isInlineFuncs: q.customIsInlineFuncs,
})
}
// Index is shorthand method to create Index and appends it.
func (q Query) Index(i int) *Query {
return q.Append(&Index{index: i})
}
// Extract extracts the value by q from target.
func (q *Query) Extract(target interface{}) (interface{}, error) {
if q == nil || len(q.extractors) == 0 {
return target, nil
}
v := reflect.ValueOf(target)
for _, e := range q.extractors {
f := e.Extract
for i := len(q.customExtractFuncs) - 1; i >= 0; i-- {
f = q.customExtractFuncs[i](f)
}
var ok bool
v, ok = f(v)
if !ok {
return nil, errors.Errorf(`"%s" not found`, q.String())
}
if v.IsValid() && !v.CanInterface() {
return nil, errors.Errorf("%s: can not access unexported field or method", q.String())
}
}
if !v.IsValid() {
return nil, nil
}
return v.Interface(), nil
}
// String returns q as string.
func (q *Query) String() string {
var b strings.Builder
if q.hasExplicitRoot {
b.WriteString("$")
}
for _, f := range q.extractors {
b.WriteString(f.String())
}
return b.String()
}
// Extractors returns query extractors of q.
func (q *Query) Extractors() []Extractor {
return q.extractors
}
// An Extractor interface is used by a query to extract the element from a value.
type Extractor interface {
Extract(v reflect.Value) (reflect.Value, bool)
String() string
}
// ExtractFunc represents a function to extracts a value.
type ExtractFunc func(v reflect.Value) (reflect.Value, bool)