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graphql.go
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graphql.go
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package main
import (
"encoding/json"
"errors"
"reflect"
"strings"
"time"
"github.com/graphql-go/graphql"
"golang.org/x/exp/constraints"
)
var typeTime = reflect.TypeOf(time.Time{})
type Pair[T1 any, T2 any] struct {
First T1
Second T2
}
func executeQuery(query string, schema graphql.Schema) (*graphql.Result, error) {
result := graphql.Do(graphql.Params{
Schema: schema,
RequestString: query,
})
if len(result.Errors) > 0 {
return nil, result.Errors[0].OriginalError()
}
return result, nil
}
func getBasicOutput(t reflect.Type) graphql.Output {
kind := t.Kind()
switch kind {
case reflect.String:
return graphql.String
case reflect.Int, reflect.Uint,
reflect.Int8, reflect.Uint8,
reflect.Int16, reflect.Uint16,
reflect.Int32, reflect.Uint32:
// Use Float since the GraphQL implementation is limited to 32-Bit.
// The resolver functions will cast the integer to float64 and return it.
// https://github.com/graphql/graphql-spec/issues/73
return graphql.Float
case reflect.Int64, reflect.Uint64:
return graphql.Float
case reflect.Bool:
return graphql.Boolean
case reflect.Float32, reflect.Float64:
return graphql.Float
default:
return nil
}
}
// Browses through the members of a given type and creates
// the corresponding field and output structure of given type.
// As an oversimplification, it works similarly to json.Marshal
// but for GraphQL.
func createGraphQlFieldHierarchy(t reflect.Type, typesMap map[string]Pair[graphql.Output, graphql.Fields], filterMap map[string]graphql.ArgumentConfig) (graphql.Output, graphql.Fields) {
// GraphQL complains when a type with the same name is registered once. Error:
// Schema must contain uniquely named types but contains multiple types named "XYZ".
//
// This can happen if a struct has two member that are of the same type:
// type Foo struct {
// X FooStruct <-- At first object type for 'FooStruct' is generated ...
// Y FooStruct <-- ... then 'FooStruct' is attempted to be generated again.
// }
//
// To avoid the error above we keep a map of all registered types and return this on a match.
if typesMap == nil {
typesMap = make(map[string]Pair[graphql.Output, graphql.Fields], 0)
}
if filterMap == nil {
filterMap = make(map[string]graphql.ArgumentConfig, 0)
}
knownType, ok := typesMap[t.Name()]
if ok {
return knownType.First, knownType.Second
}
// The code automatically transforms some types, such as time.Time, because their structure is unnecessarily complex
// for GraphQL output. For instance, the 'loc' in time.Time isn't needed and the type can be a simple timestamp.
switch t {
case typeTime:
// Return float due to the 32-bit limitations of ints
return graphql.Float, nil
}
switch t.Kind() {
case reflect.Func:
// Retrieve the return type of the function
returnType := t.Out(0)
if returnType.Kind() == reflect.Interface {
// Return type must be explicitly defined, no interface/any allowed
// as the type is used to generate the GraphQL schema.
return nil, nil
}
structFieldType, fields := createGraphQlFieldHierarchy(returnType, typesMap, filterMap)
return structFieldType, fields
case reflect.Struct:
fields := graphql.Fields{}
for _, structField := range reflect.VisibleFields(t) {
// Subfields are fields from struct subtypes.
// E.g:
// type Bar struct {
// X string <-- field 1
// Y string <-- field 2
// }
//
// type Foo struct {
// B []Bar
// }
//
// 'structField' is 'B', subfields are 'X' and 'Y'.
// They are needed to register filter resolvers for arrays/slices.
// foos(X: "abc") {
// X
// }
//
structFieldType, subfields := createGraphQlFieldHierarchy(structField.Type, typesMap, filterMap)
// Skip unsupported types
if structFieldType == nil {
continue
}
args := graphql.FieldConfigArgument{}
// Register all filter arguments
for k, v := range subfields {
switch v.Type {
case graphql.String, graphql.Int, graphql.Boolean, graphql.Float:
args[k] = &graphql.ArgumentConfig{
Type: v.Type,
}
}
}
// Value copy to ensure proper capturing of variable in Resolve closure.
// https://eli.thegreenplace.net/2019/go-internals-capturing-loop-variables-in-closures/
structFieldName := structField.Name
structFieldTypeKind := structField.Type.Kind()
switch structFieldTypeKind {
// Add helper paramters to graphql lists
case reflect.Slice, reflect.Array:
// Add where filter if the array or slice contains structs
if structField.Type.Elem().Kind() == reflect.Struct {
// Example syntax:
// items (where: {X: "abc"}) { X }
// If the filter object contains multiple fields,
// the filter will be applied as an OR operation.
// Meaning, the first item that matches any value
// of the fields will be returned.
argConfig, ok := filterMap[structFieldName]
if !ok {
fields := graphql.InputObjectConfigFieldMap{}
for _, v := range reflect.VisibleFields(structField.Type.Elem()) {
t := getBasicOutput(v.Type)
if t != nil {
fields[strings.ToLower(v.Name)] = &graphql.InputObjectFieldConfig{
Type: t,
}
}
}
argConfig = graphql.ArgumentConfig{
Type: graphql.NewInputObject(graphql.InputObjectConfig{
Name: strings.ToLower(structFieldName),
Fields: fields,
}),
}
filterMap[structFieldName] = argConfig
ok = true
}
if ok {
args["where"] = &argConfig
}
} else {
// Add skip filter
args["skip"] = &graphql.ArgumentConfig{
Type: graphql.Int,
}
// Add limit filter
args["limit"] = &graphql.ArgumentConfig{
Type: graphql.Int,
}
}
}
fields[strings.ToLower(structFieldName)] = &graphql.Field{
Name: structField.Name,
Type: structFieldType,
Args: args,
Resolve: func(p graphql.ResolveParams) (any, error) {
r := reflect.ValueOf(p.Source).FieldByName(structFieldName)
switch structFieldTypeKind {
case reflect.Func:
// Return 'null' if function field is nil
if r.IsNil() {
return nil, nil
}
// Function siganture is func() T
var err error
results := reflect.ValueOf(r.Interface()).Call([]reflect.Value{reflect.ValueOf(p.Source)})
if results[1].Interface() != nil {
err = results[1].Interface().(error)
}
return results[0].Interface(), err
case reflect.Slice, reflect.Array:
i := 0
j := r.Len()
// Evaluate the 'where' argument
filterOne, filterOneSet := p.Args["where"]
if filterOneSet {
for i := 0; i < j; i++ {
element := r.Index(i)
filter := filterOne.(map[string]interface{})
for fieldName, filterValue := range filter {
val := element.FieldByNameFunc(func(s string) bool {
return strings.ToLower(s) == fieldName
})
var match bool
// If the filter value is a number, then it is of type float64
// due to graphql.Float. See getBasicOutput.
switch filterValue.(type) {
case float64:
fv := filterValue.(float64)
rv := val.Interface()
if yFloat64, ok := rv.(float64); ok {
match = fv == yFloat64
} else if yInt, ok := rv.(int); ok {
match = fv == float64(yInt)
} else if yInt8, ok := rv.(int8); ok {
match = fv == float64(yInt8)
} else if yInt32, ok := rv.(int32); ok {
match = fv == float64(yInt32)
} else if yInt64, ok := rv.(int64); ok {
match = fv == float64(yInt64)
}
default:
match = filterValue == val.Interface()
}
if match {
return r.Slice(i, i+1).Interface(), nil
}
}
}
// item with path not found
return r.Slice(0, 0).Interface(), nil
}
// Evaluate the 'skip' argument
skip, skipOk := p.Args["skip"]
if skipOk {
i = Min(skip.(int), j-1)
}
// Evaluate the 'limit' argument
limit, limitOk := p.Args["limit"]
if limitOk {
j = Min(i+limit.(int), j)
}
return r.Slice(i, j).Interface(), nil
}
// remove r.Kind()?
switch r.Kind() {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
// Use float since graphql int is limited to 32-bit.
// Check getBasicOutput() for more info.
return float64(r.Int()), nil
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
// Use float since graphql int is limited to 32-bit.
// Check getBasicOutput() for more info.
return float64(r.Uint()), nil
case reflect.Bool:
return r.Bool(), nil
case reflect.Float32, reflect.Float64:
return r.Float(), nil
case reflect.String:
return r.Interface(), nil
case reflect.Struct:
switch r.Type() {
case typeTime:
t := r.Interface().(time.Time).UnixMilli()
return float64(t), nil
}
return r.Interface(), nil
}
return nil, errors.New("unknown type")
},
}
}
o := graphql.NewObject(graphql.ObjectConfig{
Name: t.Name(),
Fields: fields,
})
typesMap[t.Name()] = Pair[graphql.Output, graphql.Fields]{First: o, Second: fields}
return o, fields
case reflect.Array, reflect.Slice:
nt, fields := createGraphQlFieldHierarchy(t.Elem(), typesMap, filterMap)
return graphql.NewList(nt), fields
default:
return getBasicOutput(t), nil
}
}
func QueryStructViaGraphql[T any](rootField string, o T, query string) ([]byte, error) {
typ, _ := createGraphQlFieldHierarchy(reflect.TypeOf(o), nil, nil)
fields := graphql.Fields{}
fields[rootField] = &graphql.Field{
Type: typ,
Resolve: func(p graphql.ResolveParams) (any, error) {
return o, nil
},
}
rootQuery := graphql.ObjectConfig{Name: "RootQuery", Fields: fields}
schemaConfig := graphql.SchemaConfig{Query: graphql.NewObject(rootQuery)}
schema, err := graphql.NewSchema(schemaConfig)
if err != nil {
return nil, err
}
result, err := executeQuery(query, schema)
if err != nil {
return nil, err
}
b, err := json.MarshalIndent(result, "", " ")
if err != nil {
return nil, err
}
return b, nil
}
// Returns the minimum of the two given objects.
func Min[T constraints.Integer](x, y T) T {
if x < y {
return x
}
return y
}