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How to create a query with the selection of foreign objects in the field

What is the best way to query using the field value of an external object?

Suppose I have these three classes.

The UnitResult class, which describes the number of units:

@DatabaseTable
public class UnitResult {
    public static final String ID_FIELD_NAME = "id";
    public static final String UNIT_COLUMN_NAME = "unit";
    public static final String RESULT_COLUMN_NAME = "result";

    @DatabaseField(generatedId = true, columnName = ID_FIELD_NAME)
    public Integer id;

    @DatabaseField(foreign = true, canBeNull = false, columnName = UNIT_COLUMN_NAME)
    public Unit unit;

    @DatabaseField(canBeNull = true, columnName = RESULT_COLUMN_NAME)
    public Integer result = null;
}

A unit class that describes specific units in the market (e.g. jiuce, snack, etc.):

@DatabaseTable
public class Unit {
    public static final String ID_FIELD_NAME = "id";
    public static final String TYPE_FIELD_NAME = "type";

    @DatabaseField(id = true, columnName = ID_FIELD_NAME)
    public int id;

    @DatabaseField(canBeNull = false, columnName = TYPE_FIELD_NAME)
    public UnitType type;
}

And Enum of Unit type:

public enum UnitType {
    JUICES,
    DRINKS,
    SNACKS,
    NPD;
}

So how can I query everything UnitResultwhere the Unittype is UnitType.JUICES?

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1 answer

So how can I query all UnitResult where the type of Unit is UnitType.JUICES?

The way to do this in ORMLite is to use `Where.in (...) with a subquery :

// setup our sub-query on the Unit table first
QueryBuilder<Unit,Integer> uQb = unitDao.queryBuilder();
uQb.where().eq(Unit.TYPE_FIELD_NAME, UnitType.JUICES);
// outer query on UnitResult table
QueryBuilder<UnitResult,Integer> urQb = unitResultDao.queryBuilder();
// in using the sub-query
urQb.where().in(UnitResult.UNIT_COLUMN_NAME, uQb);
List<UnitResult> results = urQb.query();
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