private FieldSpec f_where() {
        return FieldSpec.builder(fluent.updateWhere(),
                "where", Modifier.PUBLIC, Modifier.FINAL)
            .initializer("new $T(this)", fluent.updateWhere())
            .build();
    }
public final UpdateWhere where = new UpdateWhere(this);

@return FieldSpec
fluent-mybatis-processor/src/main/java/cn/org/atool/fluent/processor/mybatis/filer/segment/UpdaterFiler.java