Description — Couchbase Lite concepts — Data model — Documents
    Related Content — Databases | Blobs | Indexing |


    Document Structure

    In Couchbase Lite the term 'document' refers to an entry in the database; a record, or row in a table if you like.

    Each document has an ID (primary key in other databases) by which it can be located. This ID can be automatically generated (as a UUID) or specified programmatically; the only constraints are that it must be unique within the database, and it can’t be changed. The document also has a value which contains the actual application data. This value is stored as a dictionary collection of key-value (k-v) pairs where the values themselves may comprise different types of data such as numbers, strings, arrays or even nested objects — see: Data Types

    Data Encoding

    The document body is stored in an internal, efficient, binary form ( Fleece ).
    This internal form is easily converted into a manageable native dictionary format for manipulation in applications.

    Fleece data is stored in the smallest format that will hold the value, whilst maintaining the integrity of the value.

    Data Types

    The Document class offers a set of property accessors for various scalar types, including boolean, integers, floating-point and strings. These accessors take care of converting to/from JSON encoding, and make sure you get the type you’re expecting.

    So your document content may well comprise one or more supporting data types such as:

    • Boolean

    • Date

    • Double

    • Float

    In addition to these basic data types Couchbase Lite provides for the following:

    • Dictionary — represents a read-only key-value pair collection

    • MutableDictionary — represents a writeable key-value pair collection

    • Array — represents a readonly ordered collection of objects

    • MutableArray — represents a writeable collection of objects

    • Blob — represents an arbitrary piece of binary data


    Couchbase Lite also provides for the direct handling of JSON data implemented in most cases by the provision of a toJSON() method on appropriate API classes (for example, on MutableDocument, Dictionary, Blob and Array) — see Working with JSON Data.

    Constructing a Document

    An individual document often represents a single instance of an object in application code. A document might be considered equivalent to a row in a relational table; with each of the document’s attributes being equivalent to a column.

    Documents can contain nested structures. This allows developers to express many-to-many relationships without requiring a reference or junction table; and is naturally expressive of hierarchical data.

    Most apps will work with one or more documents, persisting them to a local database and optionally syncing them, either centrally or to the cloud.

    In this section we provide an example of how you might create a hotel document, which provides basic contact details and price data.

    Data Model
    hotel: {
      type: string (value = `hotel`)
      name: string
      address: dictionary {
        street: string
        city: string
        state: string
        country: string
        code: string
      phones: array
      rate: float

    Open a Database

    First we open your database. If the database does not already exist, Couchbase Lite will create it for us.

    // Initialize the Couchbase Lite system
    // Get the database (and create it if it doesn’t exist).
    DatabaseConfiguration config = new DatabaseConfiguration();
    Database database = new Database("getting-started", config);

    See: Databases for more information

    Create a Document

    Now we create a new document to hold our application’s data.

    Because we will be adding data to the document we must use its mutable form.

    // Create your new document
    // The lack of 'const' indicates this document is mutable
    MutableDocument mutableDoc = new MutableDocument();

    For more on using Documents, see: Document Initializers and Mutability.

    Create a Dictionary

    Here we create a dictionary (address). Because we want to add values into the dictionary, we must create it in mutable form.

    When the dictionary is retrieved, each element’s value is directly accessible via its own key.

    // Create and populate mutable dictionary
    // Create a new mutable dictionary and populate some keys/values
    MutableDictionary address = new MutableDictionary();
    address.setString("street", "1 Main st.");
    address.setString("city", "San Francisco");
    address.setString("state", "CA");
    address.setString("country", "USA");
    address.setString("code"), "90210");

    For more on using Dictionaries, see: Using Dictionaries

    Create an Array

    Since our hotel may have multiple lines we provide an array (phones) to hold contact numbers. Again, because we want to add values into the array, we create it in mutable form.

    // Create and populate mutable array
    MutableArray phones = new MutableArray();

    For more on using Arrays, see: Using Arrays

    Populate a Document

    Here we add our data to the mutable document we created earlier. Each data item is stored as a key-value pair.

    // Initialize and populate the document
    // Add document type to document properties (1)
    mutable_doc.setString("type", "hotel"));
    // Add hotel name string to document properties (2)
    mutable_doc.setString("name", "Hotel Java Mo"));
    // Add float to document properties (3)
    mutable_doc.setFloat("room_rate", 121.75f);
    // Add dictionary to document's properties (4)
    mutable_doc.setDictionary("address", address);
    // Add array to document's properties (5)
    mutable_doc.setArray("phones", phones);
    1 Add hotel name (string)
    2 Add average room rate (float)
    3 Add document type (string)
    Couchbase recommend using a type attribute to define each logical document type.
    4 Add address (dictionary) The address dictionary is added to the document and stored with the key address. We will use this to retrieve it when needed.
    5 Add phone numbers (array) The phones arrary is added to the document and stored with the key phones. We will use this to retrieve it when needed.

    Save a Document

    With the document now populated, we can persist to our Couchbase Lite database, auto-generating the document id.

    // Save the document changes (1);

    Close the Database

    With our document saved, we can now close our Couchbase Lite database.

    // Close the database (1)

    Working with Data

    Checking a Document’s Properties

    To check whether a given property exists in the document, you should use the `Document.Contains(String key) method.

    If the property doesn’t exist, the call will return the default value for that getter method (0 for Document.getInt() 0.0 for Document.getFloat() etc.).

    Date accessors

    As a convenience Couchbase Lite offers Date accessors. Dates are a common data type, but JSON doesn’t natively support them, so the convention is to store them as strings in ISO-8601 format.

    Example 1. Date Getter

    This example sets the date on the createdAt property and reads it back using the Document.getDate() accessor method.

    newTask.setValue("createdAt", new Date());
    Date date = newTask.getDate("createdAt");

    Using Dictionaries

    API References
    Example 2. Read Only
    // NOTE: No error handling, for brevity (see getting started)
    Document document = database.getDocument("doc1");
    // Getting a dictionary from the document's properties
    Dictionary dict = document.getDictionary("address");
    // Access a value with a key from the dictionary
    String street = dict.getString("street");
    // Iterate dictionary
    for (String key : dict) {
        Log.i("x", "Key %s, = %s", key, dict.getValue(key));
    // Create a mutable copy
    MutableDictionary mutable_Dict = dict.toMutable();
    Example 3. Mutable
    // NOTE: No error handling, for brevity (see getting started)
    // Create a new mutable dictionary and populate some keys/values
    MutableDictionary mutable_dict = new MutableDictionary();
    mutable_dict.setString("street", "1 Main st.");
    mutable_dict.setString("city", "San Francisco");
    // Add the dictionary to a document's properties and save the document
    MutableDocument mutable_doc = new MutableDocument("doc1");
    mutable_doc.setDictionary("address", mutable_dict);;

    Using Arrays

    API References
    Example 4. Read Only
    // NOTE: No error handling, for brevity (see getting started)
    Document document = database.getDocument("doc1");
    // Getting a phones array from the document's properties
    Array array = document.getArray("phones");
    // Get element count
    int count = array.count();
    // Access an array element by index
    if (count >= 0) { String phone = array.getString(1); }
    // Iterate dictionary
    for (int i = 0; i < count; i++)
        Log.i("tag", "Item %d = %s", i, array.getString(i));
    // Create a mutable copy
    MutableArray mutable_array = array.toMutable();
    Example 5. Mutable
    // NOTE: No error handling, for brevity (see getting started)
    // Create a new mutable array and populate data into the array
    MutableArray mutable_array = new MutableArray();
    // Set the array to document's properties and save the document
    MutableDocument mutable_doc = new MutableDocument("doc1");
    mutable_doc.setArray("phones", mutable_array);;

    Using Blobs

    For more on working with blobs — see Blobs

    Document Initializers

    The following methods/initializers can be used:

    • The MutableDocument() initializer can be used to create a new document where the document ID is randomly generated by the database.

    • The MutableDocument(String id) initializer can be used to create a new document with a specific ID.

    • The Database.getDocument() method can be used to get a document. If it doesn’t exist in the database, it will return null. This method can be used to check if a document with a given ID already exists in the database.

    Example 6. Persist a document

    The following code example creates a document and persists it to the database.

    MutableDocument newTask = new MutableDocument();
    newTask.setString("type", "task");
    newTask.setString("owner", "todo");
    newTask.setDate("createdAt", new Date());
    try {;
    } catch (CouchbaseLiteException e) {
        Log.e(TAG, e.toString());


    By default, when a document is read from the database it is immutable. The `Document.toMutable() method should be used to create an instance of the document which can be updated.

    Example 7. Make a mutable document

    Changes to the document are persisted to the database when the save method is called.

    Document document = database.getDocument("xyz");
    MutableDocument mutableDocument = document.toMutable();
    mutableDocument.setString("name", "apples");
    try {;
    } catch (CouchbaseLiteException e) {
        Log.e(TAG, e.toString());
    Any user change to the value of reserved keys (_id, _rev or _deleted) will be detected when a document is saved and will result in an exception (Error Code 5 — CorruptRevisionData) — see also Document Constraints.

    Batch operations

    If you’re making multiple changes to a database at once, it’s faster to group them together. The following example persists a few documents in batch.

    Example 8. Batch operations
    try {
        database.inBatch) -> {         for (int i = 0; i < 10; i++) {             MutableDocument doc = new MutableDocument();             doc.setValue("type", "user");             doc.setValue("name", "user " + i);             doc.setBoolean("admin", false);             try {       ;             } catch (CouchbaseLiteException e) {                 Log.e(TAG, e.toString(;
                Log.i(TAG, String.format("saved user document %s", doc.getString("name")));
    } catch (CouchbaseLiteException e) {
        Log.e(TAG, e.toString());

    At the local level this operation is still transactional: no other Database instances, including ones managed by the replicator can make changes during the execution of the block, and other instances will not see partial changes. But Couchbase Mobile is a distributed system, and due to the way replication works, there’s no guarantee that Sync Gateway or other devices will receive your changes all at once.

    Document change events

    It is possible to register for document changes. The following example registers for changes to the document with ID user.john and prints the verified_account property when a change is detected.

    Example 9. Document change events
        change -> {
            Document doc = database.getDocument(change.getDocumentID());
            if (doc != null) {
                Toast.makeText(context, "Status: " + doc.getString("verified_account"), Toast.LENGTH_SHORT).show();

    Document Expiration

    Document expiration allows users to set the expiration date for a document. When the document expires, it is purged from the database. The purge is not replicated to Sync Gateway.

    Example 10. Set document expiration

    This example sets the TTL for a document to 5 minutes from the current time.

    // Purge the document one day from now
    Instant ttl =, ChronoUnit.DAYS);
    database.setDocumentExpiration("doc123", new Date(ttl.toEpochMilli()));
    // Reset expiration
    database.setDocumentExpiration("doc1", null);
    // Query documents that will be expired in less than five minutes
    Instant fiveMinutesFromNow =, ChronoUnit.MINUTES);
    Query query = QueryBuilder

    Document Constraints

    Couchbase Lite APIs do not explicitly disallow the use of attributes with the underscore prefix at the top level of document. This is to facilitate the creation of documents for use either in local only mode where documents are not synced, or when used exclusively in peer-to-peer sync.

    "_id", :"_rev" and "_sequence" are reserved keywords and must not be used as top-level attributes — see Example 11.

    Users are cautioned that any attempt to sync such documents to Sync Gateway will result in an error. To be future proof, you are advised to avoid creating such documents. Use of these attributes for user-level data may result in undefined system behavior.

    For more guidance — see: Sync Gateway - data modeling guidelines

    Example 11. Reserved Keys List
    • _attachments

    • _deleted [1]

    • _id [1]

    • _removed

    • _rev [1]

    • _sequence

    Working with JSON Data

    The toJSON() typed-accessor means you can easily work with JSON data, native and Couchbase Lite objects.


    Convert an ArrayObject to and from JSON using the toJSON() and toArray methods — see: Example 4.

    Additionally you can:

    • Initialize a 'MutableArrayObject' using data supplied as a JSON string. This is done using the init(json) constructor-- see: Example 4

    • Convert an ArrayFragment object to a JSON String

    • Set data with a JSON string using setJSON()

    Example 12. Arrays as JSON strings
    // github tag=tojson-array
    final MutableArray mArray = new MutableArray(JSON); (1)
    for (int i = 0; i < mArray.count(); i++) { (2)
        final Dictionary dict = mArray.getDictionary(i);
        System.out.println(dict.getString("name")); MutableDocument(dict.getString("id"), dict.toMap()));
    final Array features = db.getDocument("1002").getArray("features");
    for (Object feature: features.toList()) { System.out.println(feature.toString()); }
    System.out.println(features.toJSON()); (3)
    1 Initialize array with JSON string
    2 Create and save new document using the array
    3 Get native array object from new doc and print its elements
    4 Get an array from the document as a JSON string


    Convert a Blob to JSON using the toJSON method — see Example 13.

    You can also check whether a given dictionary object is a blob, or not, using isBlob() — again, see Example 13.

    Note that the blob object must first be saved to the database (generating required metadata) before you can use the toJSON method.

    Example 13. Blobs as JSON strings
    // github tag=tojson-blob
    final Map<String, ?> thisBlob = db.getDocument("thisdoc-id").toMap();
      if (!Blob.isBlob(thisBlob)) { return; }
      final String blobType = thisBlob.get("content_type").toString();
      final Number blobLength = (Number) thisBlob.get("length");

    See also: Blobs


    Convert a DictionaryObject to and from JSON using the toJSON and toDictionary methods — see Example 14.

    Additionally you can:

    • Initialize a 'MutableDictionaryObject' using data supplied as a JSON string. This is done using the init(json) constructor-- see: Example 14

    • Set data with a JSON string using setJSON()

    Example 14. Dictionaries as JSON strings
    // github tag=tojson-dictionary
    final MutableDictionary mDict = new MutableDictionary(JSON); (1)
    System.out.println("Details for: " + mDict.getString("name"));
    for (String key: mDict.getKeys()) {
        System.out.println(key + " => " + mDict.getValue(key));
    1 Set the dictionary using a JSON string


    Convert a Document to and from JSON strings using the toJSON() and setJSON() methods — see Example 15.

    Additionally you can:

    • Initialize a 'MutableDocument' using data supplied as a JSON string. This is done using the init(json) and-or init(id: json:) constructor-- see: Example 15

    • Set data with a JSON string using setJSON()

    Example 15. Documents as JSON strings
    // github tag=tojson-document
    final Query listQuery = QueryBuilder
    for (Result row: listQuery.execute()) {
        final String thisId = row.getString("metaId");
        final String json = srcDb.getDocument(thisId).toJSON(); (1)
        System.out.println("JSON String = " + json);
        final MutableDocument hotelFromJSON = new MutableDocument(thisId, json); (2)
        for (Map.Entry entry: dstDb.getDocument(thisId).toMap().entrySet()) {
            System.out.println(entry.getKey() + " => " + entry.getValue()); (3)
    1 Get a document as a JSON string
    2 Initialize a MutableDocument using the JSON string and save to a separate database
    3 Retrieve the document created from JSON and print values

    Query Results as JSON

    Convert a Query Result to JSON using its toJSON() accessor method.

    Example 16. Using JSON Results

    Use Result.toJSON() to transform your result string into a JSON string, which can easily be serialized or used as required in your application. See <> for a working example.

    // Uses Jackson JSON processor
    ArrayList<Hotel> hotels = new ArrayList<Hotel>();
    HashMap<String, Object> dictFromJSONstring;
    for (Result result : listQuery.execute()) {
      // Get result as JSON string
      String thisJsonString = result.toJSON(); (1)
            // Get Java  Hashmap from JSON string
      HashMap<String, Object> dictFromJSONstring =
              mapper.readValue(thisJsonString, HashMap.class); (2)
      // Use created hashmap
      String hotelId = dictFromJSONstring.get("id").toString();
      String hotelType = dictFromJSONstring.get("type").toString();
      String hotelname = dictFromJSONstring.get("name").toString();
      // Get custom object from Native 'dictionary' object
      Hotel thisHotel =
              mapper.readValue(thisJsonString, Hotel.class); (3)
    1 Get the Query result as a JSON string — see JSON String Format
    2 Get a native object from the JSON string
    3 Populate your custom object from the dictionary created from JSON data
    JSON String Format

    If your query selects ALL then the JSON format will be:

      database-name: {
        key1: "value1",
        keyx: "valuex"

    If your query selects a sub-set of available properties then the JSON format will be:

      key1: "value1",
      keyx: "valuex"

    1. Any change to this reserved key will be detected when it is saved and will result in a Couchbase exception (Error Code 5 — `CorruptRevisionData`)