小编Man*_*dor的帖子

我正在尝试动态构造查询,我的下一个目标是添加JOIN子句(我不知道如何使用API​​).

例如,到目前为止,这段代码对我有用:

...
Class baseClass;   
...
CriteriaBuilder cb = JpaHandle.get().getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery(this.baseClass);
Root entity_ = cq.from(this.baseClass); 
Predicate restrictions = null;
...
restrictions = cb.conjunction();
restrictions = cb.and(restrictions, entity_.get("id").in(this.listId));
...
cq.where(restrictions);
...
Query qry = JpaHandle.get().createQuery(cq);

(注意:JpaHandle来自wicket-JPA实现)

我的愿望是添加JOIN子句(尽可能通用)!

我在类中有特定的注释(this.baseClass)

例如 :

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "assay_id", nullable = false)

那么,在标准JPA中有没有这样的方法呢？(注意:这不编译)

这是一个实际的失败方法:

...
Join<Experiment,Assay> experimentAssays = entity_.join( entity_.get("assay_id") );

或者像那样:

...
CriteriaQuery<Customer> q = cb.createQuery(Customer.class);
Root<Customer> c = q.from(Customer.class);
SetJoin<Customer, PurchaseOrder> o = c.join(Customer_.orders);

对我来说,如果它可能更加通用,它会很棒......:

...
Join joinClause = …

我是 Haskell 的完全新手。我想知道为什么这个代码：

main :: IO ()
main = run theWorld presentationIO

run dom showDom = do
       event <- readCommand
       dom' <- updateDomain dom event 
       showDom dom'
       run dom' showDom

.. 不起作用以及如何解决它。错误是：

simpleExampleTextGameV.0.2.hs:96:16: error:
    • Couldn't match expected type ‘IO World’ with actual type ‘World’
    • In a stmt of a 'do' block: dom' <- updateDomain dom event
      In the expression:
        do event <- readCommand
           dom' <- updateDomain dom event
           showDom dom'
           run dom' showDom
      In an equation for ‘run’: …