JOOQ query to JOIN ON WITH clause

问题

How can I write a JOOQ query to join on a field from a "with" clause?

For example, I've tried:

create.with("a").as(select(
                           val(1).as("x"),
                           val("a").as("y")
                   ))
      .select()
      .from(tableByName("a")
      .join(ANOTHER_TABLE)
          .on(ANOTHER_TABLE.ID.eq(tableByName("a").field("x")))
      .fetch();

However, as the compiler doesn't know the type of tableByName("a").field("x") it cannot resolve which eq() method to use. Given that I know the type, is there a way I can provide it explicitly? Or is there another approach I should take to join on a field from a "with" clause?

回答1:

While I certainly agree with flutter's answer being a more desireable path to a solution here, I'll just quickly add a response that answers your specific compilation error question.

There are three things that are wrong with your current join predicate:

ANOTHER_TABLE.ID.eq(tableByName("a").field("x"))

DSL.tableByName() is deprecated. It is generally recommended to use table(Name) instead.
Such a dynamically constructed Table does not know of any of its field() references, thus table(name("a")).field("x") will return null
The compilation error is due to your ID reference being of type Field<Integer> (probably), and thus the Field.eq() method expects a Field<Integer> argument as well. Without any knowledge about the type of your field "x", the jOOQ API / Java compiler infers Field<Object>, which is invalid.

So, the solution would be to write:

// field(Name, Class)
ANOTHER_TABLE.ID.eq(field(name("a", "x"), Integer.class))

// field(Name, DataType)
ANOTHER_TABLE.ID.eq(field(name("a", "x"), ANOTHER_TABLE.ID.getDataType()))

I.e. to use DSL.field(Name, Class<T>), or DSL.field(Name, DataType<T>) if you're using custom data type bindings / converters.

回答2:

What about declaring the CTE first? Explicit common table expressions

CommonTableExpression<Record2<Integer, String>> a =
  name("a").fields("x", "y").as(select(val(1), val("a")));

create.with(a)
      .select()
      .from(a)
      .join(ANOTHER_TABLE)
      .on(ANOTHER_TABLE.ID.eq(a.field("x")))
      .fetch();

If this does not work, you can always get the DataType<?> or the Class<?> via the Field, which you can get via the Table.

来源：https://stackoverflow.com/questions/44481307/jooq-query-to-join-on-with-clause

标签

java

sql

jooq

with-clause