The method that allows JPA’s query interface to return map objects

In JPA 2.0, we can use entitymanager Createnativequery() to execute native SQL statements. However, when there is no corresponding entity class in our query result, query Getresultlist() returns a list < object [] >. That is, each row of data is returned as an array of objects.

Common usage is as follows:

This will make the code very difficult to understand. It is unknown what the element with subscript 0 is without counting the query statements. Moreover, once the query statements are adjusted, the Java code should also be adjusted together. At this time, we think that if the returned map is used, it will be much clearer.

Unfortunately, the JPA API does not provide such a setting. In fact, many underlying implementations of JPA support returning map objects.

For example:

Therefore, if we want to return the map and determine that the underlying implementation is a JPA implementation, we can take the second place and sacrifice the cross implementation features to meet our needs:

Query returns the writing method of the specified entity return type

It should be noted that using map is certainly less efficient than using object array. So you have to see if the performance degradation is acceptable. And then in my hibernate 4.2 In the environment of X, whether you write uppercase or lowercase letters in your native SQL, the returned field names are uppercase. Of course, you can process the field name in the form of custom resulttransformer, or even return the POJO you need.

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