How to create constant numeric value expression in QueryDSL?

Publish date: 2023-12-07

I'd like to create query like this with QueryDSL

update WorkMessage w set w.totalPrice = 0.12 - w.totalCost; 

I tried like this

 Expression<Float> priceExpr = Expressions.constant(0.12f); new JPAUpdateClause(em, w) .set(w.totalPrice , priceExpr.subtract(w.totalCost)); 

But this doesn't work - Expression doesn't have subtract method.

I did it like this:

 new JPAUpdateClause(em, w) .set(w.totalPrice , w.totalCost.subtract(0.12f).negate()); 

but I'd like to know how to do it the first way.

//EDit

The second way don't work:

JPAUpdateClause.toString says:

update WorkMessage workMessage set workMessage.totalPrice = -(workMessage.totalCost - :a1) 

but the SQL result is

update work_message set total_price=-total_cost-? 

Parentheses just dissapeared. Am I doing something wrong? It looks like theese:

w.totalCost.subtract(0.12f).negate() w.totalCost.negate().subtract(0.12f) 

have the same result.

For the above problem

w.totalCost.negate().add(0.12f) 

works. But I think there is a bug.

2 Answers

We removed the DSL Constant types some time ago from Querydsl. If you really want to write it the first way, then you have to express it like this :

Expressions.operation(Float.class, Ops.SUB, Expressions.constant(0.12f), w.totalCost) 

or

NumberOperation.create(Float.class, Ops.SUB, Expressions.constant(0.12f), w.totalCost) 

if you need a NumberExpression

I had the same problem some time ago (needed the constant 0), and did build my own ConstantNumberExpression class. It turned out surprisingly easy :-)

A collegue just had the same problem, for the constant 1, so I decided to post it here.

private static class ConstantNumberExpression extends NumberExpression<Integer> { private static final long serialVersionUID = 1220768215234001828L; public ConstantNumberExpression(final int constant) { super(new ConstantImpl<>(constant)); } @Override @Nullable public <R, C> R accept(final Visitor<R, C> v, @Nullable final C context) { return v.visit((Constant<Integer>) mixin, context); } } 

Of course this could be done a bit more generic, using a type parameter, but we did need it only for Integer (actually only for zero and one).

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