Function preload

callbacks/preload.go:185–351

(tx *gorm.DB, rel *schema.Relationship, conds []interface{}, preloads map[string][]interface{})

}

func preload(tx *gorm.DB, rel *schema.Relationship, conds []interface{}, preloads map[string][]interface{}) error {
	var (
		reflectValue     = tx.Statement.ReflectValue
		relForeignKeys   []string
		relForeignFields []*schema.Field
		foreignFields    []*schema.Field
		foreignValues    [][]interface{}
		identityMap      = map[string][]reflect.Value{}
		inlineConds      []interface{}
	)

	if rel.JoinTable != nil {
		var (
			joinForeignFields    = make([]*schema.Field, 0, len(rel.References))
			joinRelForeignFields = make([]*schema.Field, 0, len(rel.References))
			joinForeignKeys      = make([]string, 0, len(rel.References))
		)

		for _, ref := range rel.References {
			if ref.OwnPrimaryKey {
				joinForeignKeys = append(joinForeignKeys, ref.ForeignKey.DBName)
				joinForeignFields = append(joinForeignFields, ref.ForeignKey)
				foreignFields = append(foreignFields, ref.PrimaryKey)
			} else if ref.PrimaryValue != "" {
				tx = tx.Where(clause.Eq{Column: ref.ForeignKey.DBName, Value: ref.PrimaryValue})
			} else {
				joinRelForeignFields = append(joinRelForeignFields, ref.ForeignKey)
				relForeignKeys = append(relForeignKeys, ref.PrimaryKey.DBName)
				relForeignFields = append(relForeignFields, ref.PrimaryKey)
			}
		}

		joinIdentityMap, joinForeignValues := schema.GetIdentityFieldValuesMap(tx.Statement.Context, reflectValue, foreignFields)
		if len(joinForeignValues) == 0 {
			return nil
		}

		joinResults := rel.JoinTable.MakeSlice().Elem()
		column, values := schema.ToQueryValues(clause.CurrentTable, joinForeignKeys, joinForeignValues)
		if err := tx.Where(clause.IN{Column: column, Values: values}).Find(joinResults.Addr().Interface()).Error; err != nil {
			return err
		}

		// convert join identity map to relation identity map
		fieldValues := make([]interface{}, len(joinForeignFields))
		joinFieldValues := make([]interface{}, len(joinRelForeignFields))
		for i := 0; i < joinResults.Len(); i++ {
			joinIndexValue := joinResults.Index(i)
			for idx, field := range joinForeignFields {
				fieldValues[idx], _ = field.ValueOf(tx.Statement.Context, joinIndexValue)
			}

			for idx, field := range joinRelForeignFields {
				joinFieldValues[idx], _ = field.ValueOf(tx.Statement.Context, joinIndexValue)
			}

			if results, ok := joinIdentityMap[utils.ToStringKey(fieldValues...)]; ok {
				joinKey := utils.ToStringKey(joinFieldValues...)