Java data object JDO2.0 query language features _ MySQL

The improvement of the query language is an important part of the JDO2.0 specification. This article describes some new functions provided by JDO2.0 from a higher level. As the JDO2.0 specification has not yet entered the public draft state, nothing has been finalized yet, and everything may be subject to changes. However, JDO2.0 will soon enter the final stage, and the query feature mentioned here is the JDO2.0 Expert Group

The improvement of the query language is an important part of the JDO2.0 specification. This article describes some new functions provided by JDO2.0 from a higher level. As the JDO2.0 specification has not yet entered the public draft state, nothing has been finalized yet, and everything may be subject to changes. However, JDO2.0 will soon enter the final stage, and the query feature mentioned here is that the JDO2.0 Expert Group (Translator's note: David Jordan is an important member of the expert group) takes the most time and is relatively stable. Therefore, I have enough reason to believe that the final specification will be basically consistent with the description here.

If you think this article misses some important features, it is recommended to go to the JDO Forum immediately (http://www.jdocentral.com/forums/index.php? Showforum = 10. Here, we would like to thank Craig Russell, the leader of JDO2.0 standards, for authorizing me to publish the new features of these JDO2.0 query languages.

Query result

Let's start with the most in-depth improvements. In JDO1.0, the query result is always a set of instances of the class you specified. Consider the following UML class diagram, which expresses the relationships between four classes A, B, C, and D: