如何在JOOQ中添加多个字段以选择语句？

Question

I'm trying to add fields to select after the first initialization. It seems that there is no way to do it as it just recreates one.

String select = "actor_id,first_name,last_name,last_update";
DSLContext context = DSL.using(SQLDialect.DEFAULT);
Select select = context.select();
for (String field : select.split(",")) {
    select = context.select(field(name(field)));
}
System.out.println(select.getSQL());
// The value is always SELECT last_update ... 
// But I need select actor_id,first_name,last_name,last_update ...

I don't see a way to keep the select and then add WHERE, LIMIT etc as subsequent steps as and when required in the code flow. Should everything be done in the same step?

Something like:

select = select("test");
// code
// code
select = select("another field");
// code
// And add other sql statements to the DSL and finally get the sQL

Answer 1

in the snippet you've provided, the value of select is always "last_update" because the for-loop re-assigns select on each iteration. the last evaluated value is "last_update", so naturally, that's what select ends up being.

here's an approach that initializes the Select with the full range of columns to select, rather than building it up field-by-field:

final List<Field<?>> projection = new ArrayList<Field<?>>();

final String columnNames = "actor_id,first_name,last_name,last_update";

for(String columnName : columnNames.split(",")) {
    projection.add(field(name("Tblactor", columnName)));
}

Select query = context.select(projection);
...

hope that helps!

Answer 2

While hsl's answer shows a much better approach of storing the entire projection in a local variable, I'll just briefly comment on the mistake you made, which is simple:

SelectSelectStep select = context.select();
for (String field : select.split(",")) {

    // Your code: This always creates a new select statement from scratch
    // select = context.select(field(name(field)));

    // The code you meant to write
    select = select.select(field(name(field)));
}