scala compiling error: Cannot resolve overloaded method 'withTransaction'-CodePudding

I'm new to Scala, and I can't figure out how to solve a compiling error for method withTransaction :

Cannot resolve overloaded method 'withTransaction'

object Global {
  
   def goBootstrap(app: Application) {
    Logger.info(" ****   start *****")
     onGet();

    }

  def onGet() {
    import play.db.jpa.JPA
    Logger.info("Cnnection start");
    JPA.withTransaction(JPA.em =>
    {
      val resultsList = JPA.em.createNamedQuery("findCity").setParameter("name", "Boston").getResultList
    }
    );
    
  }

}

This code snippet is located in a Global.scala file in Play project (version 2.3.X). JPA came from import play.db.jpa.JPA

How can I solve this compiling error?

CodePudding user response：

The error is telling you that there is no method on JPA whose signature matches the parameters you're passing. You are calling JPA.withTransaction( () => Unit).

Looking at the source there are three methods withTransaction with Unit return types:

void withTransaction(Consumer<EntityManager> block);
void withTransaction(String name, Consumer<EntityManager> block);
void withTransaction(String name, boolean readOnly, Consumer<EntityManager> block);

I'm going to assume that you're trying to use the first of those methods. Looking at the docs for Consumer it requires a single argument.

In short, you need to provide an input to your block, something like:

   JPA.withTransaction(JPA.em => {
      val resultsList = JPA.em.createNamedQuery("findCity").setParameter("name", name).getResultList
    });

CodePudding user response：

The problem is that you can't directly instantiate a JPA connection through scala. Also because the play 2.3 framework does not support this feature: https://www.playframework.com/documentation/2.3.x/ScalaHome