什么是 Querydsl PathBuilder 字符串参数“变量”用于

Question

I'm working with Querydsl in my Spring Boot API for making some complex data filtering and when i declare the PathBuilder variable i've seen that first you have to pass statically your class like YourClass.class and then a string variable for the constructor as shown below:

    PathBuilder<Plan> entityPath = new PathBuilder<>(Plan.class, "plan");

So i was wondering why is necessary this string parameter and also why its name has to be the same as my class name, because when i delete it or modified it, the entityPath doesn't work.

Answer 1

A PathExpression (which PathBuilder ) is by definition represents a path variable. In your case, the path ending up in your query would be plan . Consecutively, you can build on to this path and create various path types. For example property retrieval: entityPath.get("someProperty") will return a path expression that represents plan.somePropety . So you can't create PathExpressions without an alias, because it would be essentially meaningless.

Then why this alias is not always inferred from the Path types, well simply put: because it is not related. The underlying entities used may have different naming strategies, you may want to mix up different path variables of the same type, you might reference a node that has a particular alias by itself.

The alias doesn't have to be equivalent to the simple classname, it has to be equivalent to the alias it references from any of the from/join clauses in the query.