This is experimental functionality, and as such subject to change. Use at your own risk!
Traversal
Applies to ❌ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
While the accessor methods from the model API allow for traversing the expression tree manually, a more generic way to traverse the expression tree is using the org.jooq.Traverser API, which can traverse a org.jooq.QueryPart in a similar fashion as a java.util.stream.Collector can iterate a java.util.stream.Stream, collecting and aggregating data about the expression tree. A Traverser consists of this API:
public interface Traverser<A, R> {
/**
* A supplier for a temporary data structure to accumulate {@link QueryPart}
* objects into during traversal.
*/
Supplier<A> supplier();
/**
* An optional traversal abort condition to short circuit traversal e.g.
* when the searched object has been found.
*/
Predicate<A> abort();
/**
* An optional recursion condition to prevent entering a specific
* {@link QueryPart}, e.g. when it is undesired to enter any subqueries.
*/
Predicate<QueryPart> recurse();
/**
* An optional recursion condition to prevent entering a specific
* {@link QueryPart}'s children, e.g. when it is desired to traverse only
* into certain operators.
*/
Predicate<QueryPart> recurseChildren();
/**
* A callback that is invoked before recursing into a subtree.
*/
BiFunction<A, QueryPart, A> before();
/**
* A callback that is invoked after recursing into a subtree.
*/
BiFunction<A, QueryPart, A> after();
/**
* An optional transformation function to turn the temporary data structure
* supplied by {@link #supplier()} into the final data structure.
*/
Function<A, R> finisher();
}
Some elements are similar to that of a java.util.stream.Collector, others are specific to tree traversal.
A simple illustration shows what can be done:
// Any ordinary QueryPart:
Condition condition = BOOK.ID.eq(1);
int count = condition.$traverse(
// Supplier of the initial data structure: an int
() -> 0,
// Print all traversed QueryParts and increment the counter
(r, q) -> {
System.out.println("Part " + r + ": " + q);
return r + 1;
}
);
System.out.println("Count : " + count);
The above will print:
Part 0: "BOOK"."ID" = 1 Part 1: "BOOK"."ID" Part 2: 1 Count : 3
Using the same traverser on a slightly more complex QueryPart
Condition condition = BOOK.ID.eq(1).or(BOOK.ID.eq(2)); // ...
Part 0: ("BOOK"."ID" = 1 or "BOOK"."ID" = 2)
Part 1: "BOOK"."ID" = 1
Part 2: "BOOK"."ID"
Part 3: 1
Part 4: "BOOK"."ID" = 2
Part 5: "BOOK"."ID"
Part 6: 2
Count : 7
Re-using your JDK collectors
Any Collector can be turned into a Traverser using Traversers.collecting(Collector). For example, if you want to count all QueryPart items in an expression, instead of the above hand-written traverser, just use the JDK Collectors.counting():
// Contains 3 query parts
long count1 = BOOK.ID.eq(1)
.$traverse(Traversers.collecting(Collectors.counting());
// Contains 7 query parts
long count2 = BOOK.ID.eq(1).or(BOOK.ID.eq(2))
.$traverse(Traversers.collecting(Collectors.counting());
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