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Join<Location, LocationType> locationTypeJoin = root.join(Location_.LOCATION_TYPE);
        Join<Location, Address> addressJoin = root.join(Location_.ADDRESS, JoinType.LEFT);
        Join<Address, State> stateJoin = addressJoin.join(Address_.STATE, JoinType.LEFT);
        Join<Address, County> countyJoin = addressJoin.join(Address_.COUNTY, JoinType.LEFT);

criteriaQuery.multiselect(
            root.get(Location_.LOCATION_ID), root.get(Location_.LOCATION_NAME), root.get(Location_.LOCATION_CODE),
            root.get(Location_.LAST_UPDATE_DATE_TIME), root.get(Location_.CREATE_DATE_TIME), root.get(Location_.SOURCE_SYSTEM_UNIQUE_KEY),
            joinLocationType.get(LocationType_.LOCATION_TYPE_ID), joinLocationType.get(LocationType_.LOCATION_TYPE),
            joinLocationType.get(LocationType_.LOCATION_TYPE_DESC),joinAddress.get(Address_.ADDRESS_ID));

通过joinAddress.get(Address_.ADDRESS_ID)在多选中使用上面的语句，我试图在位置表中选择表地址的外键。当我在做左连接时，对于某些行它是空的。因此，当我尝试选择它时，它会显示非法参数异常。

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1 回答 1

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我通过添加案例来检查列是否为空来解决了这个问题。

Expression<Object> case1 = criteriaBuilder.selectCase().when(criteriaBuilder.isNotNull(joinAddress.get(Address_.ADDRESS_ID)), joinAddress.get(Address_.ADDRESS_ID)).otherwise(0);
criteriaQuery.multiselect(
        root.get(Location_.LOCATION_ID), root.get(Location_.LOCATION_NAME), root.get(Location_.LOCATION_CODE),
        root.get(Location_.LAST_UPDATE_DATE_TIME), root.get(Location_.CREATE_DATE_TIME), root.get(Location_.SOURCE_SYSTEM_UNIQUE_KEY),
        joinLocationType.get(LocationType_.LOCATION_TYPE_ID), joinLocationType.get(LocationType_.LOCATION_TYPE),
        joinLocationType.get(LocationType_.LOCATION_TYPE_DESC),case1);
于 2019-05-17T06:41:03.917 回答