val = strings.ToLower(strings.TrimSpace(val))
		switch val {
		case "-":
			field.Creatable = false
			field.Updatable = false
			field.Readable = false
			field.DataType = ""
		case "all":
			field.Creatable = false
			field.Updatable = false
			field.Readable = false
			field.DataType = ""
			field.IgnoreMigration = true
		case "migration":
			field.IgnoreMigration = true

		bindName := field.BindName()
		if field.DBName != "" {
			// nonexistence or shortest path or first appear prioritized if has permission
			if v, ok := schema.FieldsByDBName[field.DBName]; !ok || ((field.Creatable || field.Updatable || field.Readable) && len(field.BindNames) < len(v.BindNames)) {
				if _, ok := schema.FieldsByDBName[field.DBName]; !ok {
					schema.DBNames = append(schema.DBNames, field.DBName)
				}

		}
	} else {
		relation.JoinTable.Relationships.Relations[relRefName].References = []*Reference{}
	}

	// build references
	for _, f := range relation.JoinTable.Fields {
		if f.Creatable || f.Readable || f.Updatable {
			// use same data type for foreign keys
			if copyableDataType(fieldsMap[f.Name].DataType) {
				f.DataType = fieldsMap[f.Name].DataType
			}
			f.GORMDataType = fieldsMap[f.Name].GORMDataType