gorm/preload.go

package gorm

import (
	"database/sql/driver"
	"errors"
	"fmt"
	"reflect"
	"strings"
)

func getRealValue(value reflect.Value, columns []string) (results []interface{}) {
	// If value is a nil pointer, Indirect returns a zero Value!
	// Therefor we need to check for a zero value,
	// as FieldByName could panic
	if pointedValue := reflect.Indirect(value); pointedValue.IsValid() {
		for _, column := range columns {
			if pointedValue.FieldByName(column).IsValid() {
				result := pointedValue.FieldByName(column).Interface()
				if r, ok := result.(driver.Valuer); ok {
					result, _ = r.Value()
				}
				results = append(results, result)
			}
		}
	}
	return
}

func equalAsString(a interface{}, b interface{}) bool {
	return fmt.Sprintf("%v", a) == fmt.Sprintf("%v", b)
}

func Preload(scope *Scope) {
	if scope.Search.preload == nil || scope.HasError() {
		return
	}

	preloadMap := map[string]bool{}
	fields := scope.Fields()
	for _, preload := range scope.Search.preload {
		schema, conditions := preload.schema, preload.conditions
		keys := strings.Split(schema, ".")
		currentScope := scope
		currentFields := fields
		originalConditions := conditions
		conditions = []interface{}{}
		for i, key := range keys {
			var found bool
			if preloadMap[strings.Join(keys[:i+1], ".")] {
				goto nextLoop
			}

			if i == len(keys)-1 {
				conditions = originalConditions
			}

			for _, field := range currentFields {
				if field.Name != key || field.Relationship == nil {
					continue
				}

				found = true
				switch field.Relationship.Kind {
				case "has_one":
					currentScope.handleHasOnePreload(field, conditions)
				case "has_many":
					currentScope.handleHasManyPreload(field, conditions)
				case "belongs_to":
					currentScope.handleBelongsToPreload(field, conditions)
				case "many_to_many":
					currentScope.handleManyToManyPreload(field, conditions)
				default:
					currentScope.Err(errors.New("not supported relation"))
				}
				break
			}

			if !found {
				value := reflect.ValueOf(currentScope.Value)
				if value.Kind() == reflect.Slice && value.Type().Elem().Kind() == reflect.Interface {
					value = value.Index(0).Elem()
				}
				scope.Err(fmt.Errorf("can't find field %s in %s", key, value.Type()))
				return
			}

			preloadMap[strings.Join(keys[:i+1], ".")] = true

		nextLoop:
			if i < len(keys)-1 {
				currentScope = currentScope.getColumnsAsScope(key)
				currentFields = currentScope.Fields()
			}
		}
	}

}

func makeSlice(typ reflect.Type) interface{} {
	if typ.Kind() == reflect.Slice {
		typ = typ.Elem()
	}
	sliceType := reflect.SliceOf(typ)
	slice := reflect.New(sliceType)
	slice.Elem().Set(reflect.MakeSlice(sliceType, 0, 0))
	return slice.Interface()
}

func (scope *Scope) handleHasOnePreload(field *Field, conditions []interface{}) {
	relation := field.Relationship

	primaryKeys := scope.getColumnAsArray(relation.AssociationForeignFieldNames)
	if len(primaryKeys) == 0 {
		return
	}

	results := makeSlice(field.Struct.Type)
	scope.Err(scope.NewDB().Where(fmt.Sprintf("%v IN (%v)", toQueryCondition(scope, relation.ForeignDBNames), toQueryMarks(primaryKeys)), toQueryValues(primaryKeys)...).Find(results, conditions...).Error)
	resultValues := reflect.Indirect(reflect.ValueOf(results))

	for i := 0; i < resultValues.Len(); i++ {
		result := resultValues.Index(i)
		if scope.IndirectValue().Kind() == reflect.Slice {
			value := getRealValue(result, relation.ForeignFieldNames)
			objects := scope.IndirectValue()
			for j := 0; j < objects.Len(); j++ {
				if equalAsString(getRealValue(objects.Index(j), relation.AssociationForeignFieldNames), value) {
					reflect.Indirect(objects.Index(j)).FieldByName(field.Name).Set(result)
					break
				}
			}
		} else {
			if err := scope.SetColumn(field, result); err != nil {
				scope.Err(err)
				return
			}
		}
	}
}

func (scope *Scope) handleHasManyPreload(field *Field, conditions []interface{}) {
	relation := field.Relationship
	primaryKeys := scope.getColumnAsArray(relation.AssociationForeignFieldNames)
	if len(primaryKeys) == 0 {
		return
	}

	results := makeSlice(field.Struct.Type)
	scope.Err(scope.NewDB().Where(fmt.Sprintf("%v IN (%v)", toQueryCondition(scope, relation.ForeignDBNames), toQueryMarks(primaryKeys)), toQueryValues(primaryKeys)...).Find(results, conditions...).Error)
	resultValues := reflect.Indirect(reflect.ValueOf(results))

	if scope.IndirectValue().Kind() == reflect.Slice {
		for i := 0; i < resultValues.Len(); i++ {
			result := resultValues.Index(i)
			value := getRealValue(result, relation.ForeignFieldNames)
			objects := scope.IndirectValue()
			for j := 0; j < objects.Len(); j++ {
				object := reflect.Indirect(objects.Index(j))
				if equalAsString(getRealValue(object, relation.AssociationForeignFieldNames), value) {
					f := object.FieldByName(field.Name)
					f.Set(reflect.Append(f, result))
					break
				}
			}
		}
	} else {
		scope.SetColumn(field, resultValues)
	}
}

func (scope *Scope) handleBelongsToPreload(field *Field, conditions []interface{}) {
	relation := field.Relationship
	primaryKeys := scope.getColumnAsArray(relation.ForeignFieldNames)
	if len(primaryKeys) == 0 {
		return
	}

	results := makeSlice(field.Struct.Type)
	scope.Err(scope.NewDB().Where(fmt.Sprintf("%v IN (%v)", toQueryCondition(scope, relation.AssociationForeignDBNames), toQueryMarks(primaryKeys)), toQueryValues(primaryKeys)...).Find(results, conditions...).Error)
	resultValues := reflect.Indirect(reflect.ValueOf(results))

	for i := 0; i < resultValues.Len(); i++ {
		result := resultValues.Index(i)
		if scope.IndirectValue().Kind() == reflect.Slice {
			value := getRealValue(result, relation.AssociationForeignFieldNames)
			objects := scope.IndirectValue()
			for j := 0; j < objects.Len(); j++ {
				object := reflect.Indirect(objects.Index(j))
				if equalAsString(getRealValue(object, relation.ForeignFieldNames), value) {
					object.FieldByName(field.Name).Set(result)
				}
			}
		} else {
			scope.SetColumn(field, result)
		}
	}
}

func (scope *Scope) handleManyToManyPreload(field *Field, conditions []interface{}) {
	var (
		relation         = field.Relationship
		joinTableHandler = relation.JoinTableHandler
		destType         = field.StructField.Struct.Type.Elem()
		linkHash         = make(map[string][]reflect.Value)
		sourceKeys       = []string{}
		foreignKeyValue  interface{}
		foreignKeyType   = reflect.ValueOf(&foreignKeyValue).Type()
		isPtr            bool
	)

	if destType.Kind() == reflect.Ptr {
		isPtr = true
		destType = destType.Elem()
	}

	for _, key := range joinTableHandler.SourceForeignKeys() {
		sourceKeys = append(sourceKeys, key.DBName)
	}

	db := scope.NewDB().Table(scope.New(reflect.New(destType).Interface()).TableName()).Select("*")

	preloadJoinDB := joinTableHandler.JoinWith(joinTableHandler, db, scope.Value)

	// preload inline conditions
	if len(conditions) > 0 {
		preloadJoinDB = preloadJoinDB.Where(conditions[0], conditions[1:]...)
	}

	rows, err := preloadJoinDB.Rows()

	if scope.Err(err) != nil {
		return
	}
	defer rows.Close()

	columns, _ := rows.Columns()
	for rows.Next() {
		var (
			elem   = reflect.New(destType).Elem()
			fields = scope.New(elem.Addr().Interface()).Fields()
		)

		// register foreign keys in join tables
		for _, sourceKey := range sourceKeys {
			fields[sourceKey] = &Field{Field: reflect.New(foreignKeyType).Elem()}
		}

		scope.scan(rows, columns, fields)

		// generate hashed forkey keys in join table
		var foreignKeys = make([]interface{}, len(sourceKeys))
		for idx, sourceKey := range sourceKeys {
			foreignKeys[idx] = fields[sourceKey].Field.Elem().Interface()
		}
		hashedSourceKeys := toString(foreignKeys)

		if isPtr {
			linkHash[hashedSourceKeys] = append(linkHash[hashedSourceKeys], elem.Addr())
		} else {
			linkHash[hashedSourceKeys] = append(linkHash[hashedSourceKeys], elem)
		}
	}

	var foreignFieldNames []string
	for _, dbName := range relation.ForeignFieldNames {
		if field, ok := scope.FieldByName(dbName); ok {
			foreignFieldNames = append(foreignFieldNames, field.Name)
		}
	}

	if scope.IndirectValue().Kind() == reflect.Slice {
		objects := scope.IndirectValue()
		for j := 0; j < objects.Len(); j++ {
			object := reflect.Indirect(objects.Index(j))
			source := getRealValue(object, foreignFieldNames)
			field := object.FieldByName(field.Name)
			for _, link := range linkHash[toString(source)] {
				field.Set(reflect.Append(field, link))
			}
		}
	} else {
		if object := scope.IndirectValue(); object.IsValid() {
			source := getRealValue(object, foreignFieldNames)
			field := object.FieldByName(field.Name)
			for _, link := range linkHash[toString(source)] {
				field.Set(reflect.Append(field, link))
			}
		}
	}
}

func (scope *Scope) getColumnAsArray(columns []string) (results [][]interface{}) {
	values := scope.IndirectValue()
	switch values.Kind() {
	case reflect.Slice:
		for i := 0; i < values.Len(); i++ {
			var result []interface{}
			for _, column := range columns {
				result = append(result, reflect.Indirect(values.Index(i)).FieldByName(column).Interface())
			}
			results = append(results, result)
		}
	case reflect.Struct:
		var result []interface{}
		for _, column := range columns {
			result = append(result, values.FieldByName(column).Interface())
		}
		return [][]interface{}{result}
	}
	return
}

func (scope *Scope) getColumnsAsScope(column string) *Scope {
	values := scope.IndirectValue()
	switch values.Kind() {
	case reflect.Slice:
		modelType := values.Type().Elem()
		if modelType.Kind() == reflect.Ptr {
			modelType = modelType.Elem()
		}
		fieldStruct, _ := modelType.FieldByName(column)
		var columns reflect.Value
		if fieldStruct.Type.Kind() == reflect.Slice || fieldStruct.Type.Kind() == reflect.Ptr {
			columns = reflect.New(reflect.SliceOf(reflect.PtrTo(fieldStruct.Type.Elem()))).Elem()
		} else {
			columns = reflect.New(reflect.SliceOf(reflect.PtrTo(fieldStruct.Type))).Elem()
		}
		for i := 0; i < values.Len(); i++ {
			column := reflect.Indirect(values.Index(i)).FieldByName(column)
			if column.Kind() == reflect.Ptr {
				column = column.Elem()
			}
			if column.Kind() == reflect.Slice {
				for i := 0; i < column.Len(); i++ {
					elem := column.Index(i)
					if elem.CanAddr() {
						columns = reflect.Append(columns, elem.Addr())
					}
				}
			} else {
				if column.CanAddr() {
					columns = reflect.Append(columns, column.Addr())
				}
			}
		}
		return scope.New(columns.Interface())
	case reflect.Struct:
		field := values.FieldByName(column)
		if !field.CanAddr() {
			return nil
		}
		return scope.New(field.Addr().Interface())
	}
	return nil
}