Grouping with Parentheses
and Repeating Field Names
in Recursion

RQL Provides OOP Notation and Automatically Resolves Recursion for Object Queries

RQL supports a very flexible syntax for writing query expressions.

Grouping with parallel and nested parentheses.
A query variable can appear multiple times within a query expression.
A wide variety of logical operators are available for objects, although only a few can be presented on these pages at this time.

Query Example 1: The query variable Q2 is used twice, and grouping with parentheses is demonstrated in the code extract below.

    RootStore r1 = rdb.getRootStore("fi.rootrql.example1.Person");
    Query query = Query.createQuery()
                .addQ1Query(r1, "(((Q2 AND Q3) OR (Q4 AND Q5)) MERGE"
            + "(Q6 OR (Q2 AND (friends.hobby IN ('slalom','rally')))))")
                .addQ2Query(r1, " ... query expression Q2 ...")
                .addQ3Query(r1, " ... query expression Q3 ...")
                .addQ4Query(r1, " ... query expression Q4 ...")
                .addQ5Query(r1, " ... query expression Q5 ...")
                .addQ6Query(r1, " ... query expression Q6 ...");
    List<Person> list = query.queryQ1Objects();

In a recursive data structure, the same field name can be repeated multiple times within a query expression.

Query Example 2: The field name friends is repeated three times in the query condition.

    RootStore r1 = rdb.getRootStore("fi.rootrql.users.Person");
    Query query = Query.createQuery()
            .setParts(true)
            .addQ1Query(r1, "(friends.friends.friends.hobby = 'golf')");
    List<Person> list = query.queryQ1Objects();

Query Example 3: The dot notation of OOP can be used just as in object-oriented programming to define the location of the search condition within the data structure.

    RootStore r1 = rdb.getRootStore("fi.rootrql.users.Person");
    Query query = Query.createQuery()
            .setParts(true)
            .addQ1Query(r1, "(" +
                "friends.organization.friends.friends.hobby = 'golf')");
    List<Person> list = query.queryQ1Objects();

However, a more general and better option is to use the setResolveRoots attribute with the value set to true.

Root objects are automatically resolved for the query result objects.
A class and its inheritance hierarchy can have multiple fields that recursively reference themselves or other classes within the inheritance hierarchy.
All root objects are resolved if multiple root objects exist.
Object cycles (loops) within data structures are also automatically resolved.

RQL Query 3: Calling the method setQ1ResolveRoots(true) specifies that all root objects are automatically resolved for the query result objects within the recursive data structure of the Person class. The attribute setQ1ResolveCycles is also set, although the default value is already true.

    RootStore r1 = rdb.getRootStore("fi.rootrql.users.Person");
    Query query = Query.createQuery()
                    .setParts(true)
                    .addQ1Query(r1, "(friends.hobby = 'golf')")
                    .setQ1ResolveRoots(true)
                    .setQ1ResolveCycles(true) //true is also default value
    List<Person> list = query.queryQ1Objects();

The automatic resolution of recursive data structures in database searches offers significant advantages.

Resolving inheritance is incorporated into resolving recursion.
The depth of recursion is typically unknown in advance.
Repeating the field name can be seen as a special case of automatic recursion resolution, as it can only resolve objects in a single location within the data structure.
The performance is very good in resolving recursive data structures.
In fact, the use of recursion is encouraged when designing object models for RootDB databases.

Links to other pages on this site.

Query with Inheritance and Recursion
A Completely New Query Category that Efficiently Resolves the Data Structures of Search Results
RootDB, Technical Features
RootDB and RQL, Home

Grouping with Parentheses and Repeating Field Names in Recursion

RQL Provides OOP Notation and Automatically Resolves Recursion for Object Queries

Grouping with Parentheses
and Repeating Field Names
in Recursion