How to Query Entitys from the Database?

A simple example of a query that matches all documents with the title Thesis is defined like this:

 Query q = new QueryEquals(Document.SCHEMA.prototype().title, "Thesis");
 

Now all results can be iterated:

 for (Document d : Document.SCHEMA.queryEntities(q)) {
     System.out.println("match: " + d);
 }
 

 Query q = new QueryAll();
 q.addSortingCriterion(new Ascending(Document.SCHEMA.prototype().title));
 

How to Formulate Joins

As shown in the picture, a QueryCondition referes to instances of the interface Attribute. Since the superclass Property implements this interface, all properties can be used to formulate a query condition.

Relationships are defined using Roles, so it is necessary to get an instance of Attribute from a role in order to define a join query.

This is done by the method Role.getAttributeSignature(). This method returns the foreign key column which realizes the role in the relational database as an instance of Attribute, and can then be used to build complex join queries.

Doing so requires some knowledge about the relational mapping of the data model (see ObjectRelationalMappingDoc).

Constructor Summary

Method Summary

Constructor Detail

public Query()

Method Detail

public abstract Object visit(QueryVisitor v)

public void addJoin(Join q2)

public List getJoins()

public void addSortingCriterion(SortingCriterion c)

public List getAllSortingCriterions()

public String toString()