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# Queries

The Query API is deprecated and the search API should be used instead.

As is custom for every framework, querying the model must be possible. Strolch queries are implemented using the `StrolchQuery` interface and one of its concrete implementations: `ResourceQuery`, `OrderQuery`, `ActivityQuery`.

A Strolch element always has two identifiers: `Type` and `Id`. The type is important as it classifies an element. So if a car and a house would be modelled in Strolch, then those would both be a `Resource`, but one of type `Car` and the other of type `House`. Both would have different parameters.

Thus one of the inputs for every query is it’s type, which is defined as the navigation. It is said that we navigate to the Cars, or Houses. Thus when instantiating a ResourceQuery, pass the navigation to the type of Resource as well. Same applies for Orders and Activities.

Further input for a StrolchQuery are the selections. These selections get translated into RDBMS `WHERE` clauses. Selections support boolean operations thus allowing for complex querying.

StrolchQueries also support Ordering and object transformation. Following classes provide the most used scenarios:

- OrderById
- OrderByName
- OrderByParameter
- *ToDomVisitor
- *ToSaxVisitor
- *ToJsonVisitor
- *ToFlatJsonVisitor

Example: Query all resources of type Car:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<Resource> query = ResourceQuery.query("Car");
      query.withAny();
      List<Resource> cars = tx.doQuery(query);
    }

Example: Query all resources of type Car, order by Name and transform to JSON:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<JsonObject> query = ResourceQuery.query("Car", new ResourceToJsonVisitor(),
          new OrderByName());
      query.withAny();
      List<JsonObject> cars = tx.doQuery(query);
    }

the previous example can also be written as follows:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<JsonObject> query = new ResourceQuery<>();
      query.setNavigation(new StrolchTypeNavigation("Car"));
      query.setResourceVisitor(new ResourceToJsonVisitor());
      query.withAny();
      List<JsonObject> cars = tx.doQuery(query);
    }

Example: Query all resources of type Car with color blue:

    try (StrolchTransaction tx = openTx()) {
        ResourceQuery<Resource> query = ResourceQuery.query("Car");
        query.with(ParameterSelection.stringSelection("parameters", "color", "blue", StringMatchMode.es()));
        List<Resource> cars = tx.doQuery(query);
    }

Example: Query all resources of type Car which are not blue:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<Resource> query = ResourceQuery.query("Car");
      query.not(ParameterSelection.stringSelection("parameters", "color", "blue", StringMatchMode.es()));
      List<Resource> cars = tx.doQuery(query);
    }

Example: Query all resources of type Car with color blue or yellow:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<Resource> query = ResourceQuery.query("Car");
      query.or().with(
          ParameterSelection.stringSelection("parameters", "color", "blue", StringMatchMode.es()),
          ParameterSelection.stringSelection("parameters", "color", "yellow", StringMatchMode.es()));
      List<Resource> cars = tx.doQuery(query);
    }

Example: Query all resources of type Car with color blue or yellow owned by Jill:

    try (StrolchTransaction tx = openTx()) {
      ResourceQuery<Resource> query = ResourceQuery.query("Car");

      StringParameterSelection owner = ParameterSelection.stringSelection("parameters", "owner", "Jill", StringMatchMode.es());
      OrSelection colors = new OrSelection().with(
          ParameterSelection.stringSelection("parameters", "color", "blue", StringMatchMode.es()),
          ParameterSelection.stringSelection("parameters", "color", "yellow", StringMatchMode.es()));

      query.and().with(owner, colors);

      List<Resource> cars = tx.doQuery(query);
    }