Query Models

A QueryModel is purely an ORM object that maps rows from a Cursor into a Model such that when loading from the DB, we can easily use the data from it.

We use a different annotation, @QueryModel, to define it separately. These do not allow for modifications in the DB, rather act as a marshal agent out of the DB.

Define a QueryModel

For this example, we have a list of employees that we want to gather the average salary for each position in each department from our company.

We defined an Employee table:

@Table(database = AppDatabase.class)
public class EmployeeModel {

    @PrimaryKey
    String uid;

    @Column
    long salary;

    @Column
    String name;

    @Column
    String title;

    @Column
    String department;
}

We need someway to retrieve the results of this query, since we want to avoid dealing with the Cursor directly. We can use a SQLite query with our existing models, but we have no way to map it currently to our tables, since the query returns new Columns that do not represent any existing table:

SQLite.select(EmployeeModel_Table.department,
                Method.avg(EmployeeModel_Table.salary.as("average_salary")),
                EmployeeModel_Table.title)
      .from(EmployeeModel.class)
      .groupBy(EmployeeModel_Table.department, EmployeeModel_Table.title);

So we must define a QueryModel, representing the results of the query:

@QueryModel(database = AppDatabase.class)
public class AverageSalary {

    @Column
    String title;

    @Column
    long average_salary;

    @Column
    String department;
}

And adjust our query to handle the new output:

SQLite.select(EmployeeModel_Table.department,
                Method.avg(EmployeeModel_Table.salary.as("average_salary")),
                EmployeeModel_Table.title)
      .from(EmployeeModel.class)
      .groupBy(EmployeeModel_Table.department, EmployeeModel_Table.title)
      .async()
      .queryResultCallback(new QueryTransaction.QueryResultCallback<EmployeeModel>() {
          @Override
          public void onQueryResult(QueryTransaction transaction, @NonNull CursorResult<EmployeeModel> tResult) {
              List<AverageSalary> queryModels = tResult.toCustomListClose(AverageSalary.class);

            // do something with the result
          }
      }).execute();

Query Model Support

QueryModel support only a limited subset of Model features.

If you use the optional base class of BaseQueryModel, Modifications such as insert(), update(), save(), and delete() will throw an InvalidSqlViewOperationException. Otherwise, RetrievalAdapter do not contain modification methods.

They support allFields and inheritance and visibility modifiers as defined by Models.

QueryModel do not support:

1. InheritedField/InheritedPrimaryKey
2. @PrimaryKey/@ForeignKey
3. caching
4. changing "useBooleanGetterSetters" for private boolean fields.