Getting dynamic property predicate by property name with queryDSL

Question

I using Query DSL generated entity EntitySerializer in order to query JPA entities using QueryDSL (integrated with SpringData).

I’m receiving from the client property names and I want to create predicates for the properties that can be added (AND) to additional predicats.

I don’t know how to get from the EntitySerializer the predicate/Path that matches my property name. For example, let’s say we have a Person entity (with auto generated QPerson class) with a “name” property that I want to filter on (at the end I want to create a generic method). Here is the generic method:

Public Predicat getPredicatByPropertyName(String propertyName)  {
      QPerson p = QPerson.person;
      person.getPredicat(“propertyName”).like(“tom”);
}

score 6 · Accepted Answer · answered Nov 15 '12 at 07:31

6

To create a String typed property just use the following snippet

new StringPath(p, propertyName)

which can then be used like this to create a Predicate instance

new StringPath(p, propertyName).like("tom")

answered Nov 15 '12 at 07:31

Timo Westkämper

21,824
5
78
111

this way should check the property's type before and then do a switch, not good enough. – sendreams Mar 25 '16 at 07:44
method has protected access – Thanos M Jan 25 '22 at 13:48

score 6 · Answer 2 · answered Dec 17 '15 at 16:44

I did it slightly different since as Timo said didn't work straightforward, here is it:

query.from(play);
query.where( Expressions.stringPath(play, "name").eq("New play") );

I know it could also be achieved by doing it separately:

StringPath column = Expressions.stringPath(play, "name");

query.from(play);
query.where( column.eq("New play") );

score 0 · Answer 3 · answered Oct 18 '22 at 13:37

As of QueryDSL 5.0, I found two ways to do this independent of the column class:

First way: using just reflection:

Field pathField = p.getClass().getField(reportField.getFieldName());
ComparableExpressionBase<?> path = (ComparableExpressionBase<?>)
pathField.get(p);

Note: I use the ComparableExpressionBase class because it is extendend by all "path classes" that I found and it also can be used in select, orderBy and other functions to build the query

Second way: using reflection and ExpressionUtils:

Class<?> pParameterClass = (Class<?>) ((ParameterizedType) p.getClass().getGenericSuperclass())
            .getActualTypeArguments()[0];
Class<?> pathClass = pParameterClass.getDeclaredField(pathName).getDeclaringClass();
Path<?> path = ExpressionUtils.path(pathClass, p, pathName);

Note: using this way we first get the class of the entity of the table see this answer for an explanation on how to get a parametrized type. Next, we get the class of the path and finally we get the path with the ExpressionUtils.path method.

Getting dynamic property predicate by property name with queryDSL

3 Answers3