Finding Entities

Finding entities in Active Objects is done through the EntityManager find methods.

Finding all entities

The simplest one will return all entities of a given type. This is as simple as:

  entityManager.find(Post.class);

Here all the posts are going to be returned. Note that by default Active Object is lazy and therefore only IDs of the posts are going to be loaded. However it might still not be wise to load all the entities of a given type at once.

Finding entities with a given criteria

Adding a criteria is as simple as writing a SQL where clause. Here is what we would write to get the posts published between two dates:

  entityManager.find(Post.class, Query.select().where("published > ? AND published < ?", date1, date2));

Note how we made used of the ? placeholder just as when using JDBC's prepared statements. It is preferable to appending strings directly which might make the code prone to SQL injection.

We've made used of the Query object here, but EntityManager provides a shortcut that allows us to write that same query like this:

  entityManager.find(Post.class, "published > ? AND published < ?", date1, date2);

Finding entities with like

Adding a wildcard is also much like a SQL Query, here is what we would write to get a (contrived) field that is like the argument:

  entityManager.find(Post.class, Query.select().where("SOME_FIELD LIKE ?", "%" + arg));

Note:

The naming of column is configured via the FieldNameConverter. When using the ActiveObjects plugin this is configured for you and column names used in queries should match the strategy used.

The case is especially important when working with databases such as Postgres – which is one of the supported databases. See those FAQ entries for the strategy used in the Active Objects plugin:

Ordering elements returned

The order of returned element is not guaranteed by default in SQL, so here is how to apply the order clause when using Active Objects:

  entityManager.find(Post.class, Query.select().order("published DESC"));

Limiting the number of elements returned, and paging

There is also the possibility to limit the number of entities returned:

  entityManager.find(Post.class, Query.select().limit(10).offset(9));

This query also starts selecting the elements from the 9th in the given order (which is not specified here). It is a good idea to specify a given order when using offset and limit for paging.

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