Basic Object Retrieval

Backendless supports multiple data search and retrieval operations. These include finding an object by its objectId, finding first or last object in the collection or retrieving the entire persisted collection. Each method is available in both blocking and non-blocking formats:

Retrieving Data Objects

Blocking API

Using Java MapCustom Class

Retrieve data objects with the default paging setting from a table:

public List<Map> Backendless.Data.of( "TABLE-NAME" ).find()

Find first data object from a table. The first data object is the first one saved in the data store:

public Map Backendless.Data.of( "TABLE-NAME" ).findFirst()

Find last data object from a table. The last data object is the last one saved in the data store:

public Map Backendless.Data.of( "TABLE-NAME" ).findLast()

Find a data object by its ID:

public Map Backendless.Data.of( "TABLE-NAME" ).findById( String objectId )

Retrieve data objects with the default paging setting from a table. Returned collection will contain objects of type E (the name of the class must match the name of the table):

public List<E> Backendless.Data.of( E ).find()

Find first data object of class E. The first data object is the first one saved in the data store:

public E Backendless.Data.of( E ).findFirst()

Find last data object of type E. The last data object is the last one saved in the data store:

public E Backendless.Data.of( E ).findLast()

Find a data object by its ID:

public E Backendless.Data.of( E ).findById( String objectId )

Non-Blocking API

Using Java MapCustom Class

Retrieve data objects with the default paging setting from a table:

public void Backendless.Data.of( "TABLE-NAME" ).find( AsyncCallback<List<Map>> responder )

Find first data object from a table. The first data object is the first one saved in the data store:

public void Backendless.Data.of( "TABLE-NAME" ).findFirst( AsyncCallback<Map> responder )

Find last data object from a table. The last data object is the last one saved in the data store:

public void Backendless.Data.of( "TABLE-NAME" ).findLast( AsyncCallback<Map> responder )

Find a data object by its objectId:

public void Backendless.Data.of( "TABLE-NAME" ).findById( String objectId, 
                                                                 AsyncCallback<Map> responder )

Retrieve data objects with the default paging setting from a table. Returned collection will contain objects of type E (the name of the class must match the name of the table):

public void Backendless.Persistence.of( E ).find( AsyncCallback<List<E>> responder );

Find first data object from a table. The name of the class E must match the name of the table. The first data object is the first one saved in the data store:

public void Backendless.Persistence.of( E ).findFirst( AsyncCallback<E> responder )

Find last data object from a table. The name of the class E must match the name of the table. The last data object is the last one saved in the data store:

public void Backendless.Persistence.of( E ).findLast( AsyncCallback<E> responder )

Find a data object by its ID. The name of the class E must match the name of the table:

public void Backendless.Persistence.of( E ).findById( String objectId, 
                                                      AsyncCallback<E> responder )

where:

Argument	Description
TABLE-NAME	Name of the table from where the data is retrieved from.
E	Java class identifying the table where from where the data must be loaded from. For example, if the table is "Person", the argument should Person.class.
responder	a responder object which will receive a callback when the method successfully returns a result or an error. Applies to the asynchronous methods only.

Example

Using Java Map

The following code demonstrates various search queries:

Load contacts using default paging

**Blocking API**
``` java
List<Map> result = Backendless.Data.of( "Contact" ).find();
```

**Non-Blocking API**
``` java
Backendless.Data.of( "Contact" ).find( new AsyncCallback<List<Map>>(){
  @Override
  public void handleResponse( List<Map> foundContacts )
  {
    // every loaded object from the "Contact" table is now an individual java.util.Map
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find first contact

**Blocking API**
``` java
Map firstContact = Backendless.Data.of( "Contact" ).findFirst();
```

**Non-Blocking API**
``` java
Backendless.Data.of( "Contact" ).findFirst( new AsyncCallback<Map>(){
  @Override
  public void handleResponse( Map contact )
  {
    // first contact instance has been found
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find last contact

**Blocking API**
``` java
Map firstContact = Backendless.Data.of( "Contact" ).findLast();
```

**Non-Blocking API**
``` java
Backendless.Data.of( "Contact" ).findLast( new AsyncCallback<Map>(){
  @Override
  public void handleResponse( Map contact )
  {
    // last contact instance has been found
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find contact by objectId

**Blocking API**
``` java
// Save a contact object first. Once it is saved, we will retrieve it by assigned objectId
HashMap contact = new HashMap();
contact.put( "name", "Jack Daniels" );
contact.put( "age", 147 );
contact.put( "phone", "777-777-777" );
contact.put( "title", "Favorites" );

// save object synchronously
Map savedContact = Backendless.Data.of( "Contact" ).save( contact );

// now retrieve the object using it's objectId
Map lastContact = Backendless.Data.of( "Contact" ).
                                    findById( savedContact.get( "objectId" ) );
```

**Non-Blocking API**
``` java
// Save a contact object first. Once it is saved, we will retrieve it by assigned objectId
HashMap contact = new HashMap();
contact.put( "name", "Jack Daniels" );
contact.put( "age", 147 );
contact.put( "phone", "777-777-777" );
contact.put( "title", "Favorites" );

Backendless.Data.of( "Contact" ).save( contact, new AsyncCallback<Map>()
{
  @Override
  public void handleResponse( Map savedContact )
  {
    // now that the object is saved and has objectId, retrieve it using "findById"
    Backendless.Data.of( Contact.class ).findById( savedContact.get( "objectId" ), 
                                                          new AsyncCallback<Map>() {
      @Override
      public void handleResponse( Map response )
      {
        // an object from the "Contact" table has been found by it's objectId
      }
      @Override
      public void handleFault( BackendlessFault fault )
      {
        // an error has occurred, the error code can be retrieved with fault.getCode()
      }
    } );
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
} );
```

Custom Class

Consider the following class:

package com.sample;

public class Contact
{
  private String objectId;
  private String name;
  private int age;
  private String phone;
  private String title;

  public String getObjectId() {
    return objectId;
  }

  public void setObjectId( String objectId ) {
    this.objectId = objectId;
  }

  public String getName() {
    return name;
  }

  public void setName( String name ) {
    this.name = name;
  }

  public int getAge() {
    return age;
  }

  public void setAge( int age ) {
    this.age = age;
  }

  public String getPhone() {
    return phone;
  }

  public void setPhone( String phone ) {
    this.phone = phone;
  }

  public String getTitle() {
    return title;
  }

  public void setTitle( String title ) {
    this.title = title;
  }
}

The following code demonstrates various search queries:

Load contacts using default paging

**Blocking API**
``` java
List<Contact> result = Backendless.Data.of( Contact.class ).find();
```

**Non-Blocking API**
``` java
Backendless.Data.of( Contact.class).find( new AsyncCallback<List<Contact>>(){
  @Override
  public void handleResponse( List<Contact> foundContacts )
  {
    // all Contact instances have been found
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find first contact

**Blocking API**
``` java
Contact firstContact = Backendless.Data.of( Contact.class ).findFirst();
```

**Non-Blocking API**
``` java
Backendless.Data.of( Contact.class).findFirst( new AsyncCallback<Contact>(){
  @Override
  public void handleResponse( Contact contact )
  {
    // first contact instance has been found
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find last contact

**Blocking API**
``` java
Contact lastContact = Backendless.Data.of( Contact.class ).findLast();
```

**Non-Blocking API**
``` java
Backendless.Data.of( Contact.class).findLast( new AsyncCallback<Contact>(){
  @Override
  public void handleResponse( Contact contact )
  {
    // last contact instance has been found
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
});
```

---

Find contact by objectId

**Blocking API**
``` java
// Save a contact object first. Once it is saved, we will retrieve it by assigned objectId
Contact contact = new Contact();
contact.setName( "Jack Daniels" );
contact.setAge( 147 );
contact.setPhone( "777-777-777" );
contact.setTitle( "Favorites" );

// save object synchronously
Contact savedContact = Backendless.Data.save( contact );

// now retrieve the object using it's objectId
Contact foundContact = Backendless.Data.of( Contact.class ).findById( savedContact.getObjectId() );
```

**Non-Blocking API**
``` java
// Save a contact object first. Once it is saved, we will retrieve it by assigned objectId
Contact contact = new Contact();
contact.setName( "Jack Daniels" );
contact.setAge( 147 );
contact.setPhone( "777-777-777" );
contact.setTitle( "Favorites" );

Backendless.Data.save( contact, new AsyncCallback<Contact>()
{
  @Override
  public void handleResponse( Contact savedContact )
  {
    // now that the object is saved and has objectId, retrieve it using "findById"
    Backendless.Persistence.of( Contact.class ).findById( savedContact.getObjectId(), 
                                                          new AsyncCallback<Contact>() {
      @Override
      public void handleResponse( Contact response )
      {
        // a Contact instance has been found by objectId
      }
      @Override
      public void handleFault( BackendlessFault fault )
      {
        // an error has occurred, the error code can be retrieved with fault.getCode()
      }
    } );
  }
  @Override
  public void handleFault( BackendlessFault fault )
  {
    // an error has occurred, the error code can be retrieved with fault.getCode()
  }
} );
```