http://ebean-orm.github.io/: For open source java artifacts.
  • Rob Bygrave 
package io.ebean;

import javax.annotation.Nonnull;


Defines what part of the object graph to load (select and fetch clauses).


Using a FetchGroup effectively sets the select() and fetch() clauses for a query. It is alternative
to specifying the select() and fetch() clauses on the query allowing for more re-use of "what to load"
that can be defined separately from the query and combined with other FetchGroups.



Select example



FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class, "name, status");
Customer.query()
  .select(fetchGroup)
  .findList();



Select and fetch example



FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class)
  .select("name, status")
  .fetch("contacts", "firstName, lastName, email")
  .build();
Customer.query()
  .select(fetchGroup)
  .findList();



Combining FetchGroups



  FetchGroups can be combined together to form another FetchGroup.




 FetchGroup<Address> FG_ADDRESS = FetchGroup.of(Address.class)
   .select("line1, line2, city")
   .fetch("country", "name")
   .build();
 FetchGroup<Customer> FG_CUSTOMER = FetchGroup.of(Customer.class)
   .select("name, version")
   .fetch("billingAddress", FG_ADDRESS)
   .build();
 Customer.query()
   .select(FG_CUSTOMER)
   .findList();



Type parameters:
  • <T> – The bean type the Fetch group can be applied to
/**
 * Defines what part of the object graph to load (select and fetch clauses).
 * <p>
 * Using a FetchGroup effectively sets the select() and fetch() clauses for a query. It is alternative
 * to specifying the select() and fetch() clauses on the query allowing for more re-use of "what to load"
 * that can be defined separately from the query and combined with other FetchGroups.
 * </p>
 *
 * <h3>Select example</h3>
 * <pre>{@code
 *
 * FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class, "name, status");
 *
 * Customer.query()
 *   .select(fetchGroup)
 *   .findList();
 *
 * }</pre>
 *
 * <h3>Select and fetch example</h3>
 * <pre>{@code
 *
 * FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class)
 *   .select("name, status")
 *   .fetch("contacts", "firstName, lastName, email")
 *   .build();
 *
 * Customer.query()
 *   .select(fetchGroup)
 *   .findList();
 *
 * }</pre>
 *
 * <h3>Combining FetchGroups</h3>
 * <p>
 *   FetchGroups can be combined together to form another FetchGroup.
 * </p>
 * <pre>{@code
 *
 *  FetchGroup<Address> FG_ADDRESS = FetchGroup.of(Address.class)
 *    .select("line1, line2, city")
 *    .fetch("country", "name")
 *    .build();
 *
 *  FetchGroup<Customer> FG_CUSTOMER = FetchGroup.of(Customer.class)
 *    .select("name, version")
 *    .fetch("billingAddress", FG_ADDRESS)
 *    .build();
 *
 *
 *  Customer.query()
 *    .select(FG_CUSTOMER)
 *    .findList();
 *
 * }</pre>
 *
 * @param <T> The bean type the Fetch group can be applied to
 */
public interface FetchGroup<T> {

  
Return the FetchGroup with the given select clause.


  We use this for simple FetchGroup that only select() properties and do not have additional fetch() clause.




FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class, "name, status");
Customer.query()
  .select(fetchGroup)
  .findList();



Params:
  • select – The select clause of the FetchGroup
Returns:The FetchGroup with the given select clause
/**
   * Return the FetchGroup with the given select clause.
   * <p>
   *   We use this for simple FetchGroup that only select() properties and do not have additional fetch() clause.
   * </p>
   * <pre>{@code
   *
   * FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class, "name, status");
   *
   * Customer.query()
   *   .select(fetchGroup)
   *   .findList();
   *
   * }</pre>
   *
   * @param select The select clause of the FetchGroup
   *
   * @return The FetchGroup with the given select clause
   */
  @Nonnull
  static <T> FetchGroup<T> of(Class<T> cls, String select) {
    return XServiceProvider.fetchGroupOf(cls, select);
  }

  
Return the FetchGroupBuilder with the given select clause that we can add fetch clauses to.


We chain select() with one or more fetch() clauses to define the object graph to load.




FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class)
  .select("name, status")
  .fetch("contacts", "firstName, lastName, email")
  .build();
Customer.query()
  .select(fetchGroup)
  .findList();



Returns:The FetchGroupBuilder with the given select clause which we will add fetch clauses to
/**
   * Return the FetchGroupBuilder with the given select clause that we can add fetch clauses to.
   * <p>
   * We chain select() with one or more fetch() clauses to define the object graph to load.
   * </p>
   * <pre>{@code
   *
   * FetchGroup<Customer> fetchGroup = FetchGroup.of(Customer.class)
   *   .select("name, status")
   *   .fetch("contacts", "firstName, lastName, email")
   *   .build();
   *
   * Customer.query()
   *   .select(fetchGroup)
   *   .findList();
   *
   * }</pre>
   *
   * @return The FetchGroupBuilder with the given select clause which we will add fetch clauses to
   */
  @Nonnull
  static <T> FetchGroupBuilder<T> of(Class<T> cls) {
    return XServiceProvider.fetchGroupOf(cls);
  }

}