Predictive Query — Working with Queries


    Description — Couchbase Lite database data querying concepts — predictive query
    Related Content — Indexing | Live Query | Queries


    Enterprise Edition only
    Predictive Query is an Enterprise Edition feature.

    Predictive Query enables Couchbase Lite queries to use machine learning, by providing query functions that can process document data (properties or blobs) via trained ML models.

    Let’s consider an image classifier model that takes a picture as input and outputs a label and probability.

    predictive diagram

    To run a predictive query with a model as the one shown above, you must implement the following steps.

    Integrate the Model

    To integrate a model with Couchbase Lite, you must implement the PredictiveModel interface which has only one function called predict().

    // `tensorFlowModel` is a fake implementation
    // this would be the implementation of the ml model you have chosen
    class ImageClassifierModel implements PredictiveModel {
        public Dictionary predict(@NonNull Dictionary input) {
            Blob blob = input.getBlob("photo");
            if (blob == null) { return null; }
            // `tensorFlowModel` is a fake implementation
            // this would be the implementation of the ml model you have chosen
            return new MutableDictionary(TensorFlowModel.predictImage(blob.getContent())); (1)
    class TensorFlowModel {
        public static Map<String, Object> predictImage(byte[] data) {
            return null;
    1 The predict(input) -> output method provides the input and expects the result of using the machine learning model. The input and output of the predictive model is a DictionaryObject. Therefore, the supported data type will be constrained by the data type that the DictionaryObject supports.

    Register the Model

    To register the model you must create a new instance and pass it to the Database.prediction.registerModel static method.

    Database.prediction.registerModel("ImageClassifier", new ImageClassifierModel());

    Create an Index

    Creating an index for a predictive query is highly recommended. By computing the predictions during writes and building a prediction index, you can significantly improve the speed of prediction queries (which would otherwise have to be computed during reads).

    There are two types of indexes for predictive queries:

    Value Index

    The code below creates a value index from the "label" value of the prediction result. When documents are added or updated, the index will call the prediction function to update the city value in the index.

    ValueIndex index = IndexBuilder.valueIndex(ValueIndexItem.expression("label")));
    database.createIndex("value-index-image-classifier", index);

    Predictive Index

    Predictive Index is a new index type used for predictive query. The Predictive Index is different from the value index in that the Predictive Index caches the predictive result and creates the value index from the cached predictive result when the predictive results values are specified.

    The code below creates a predictive index from the "label" value of the prediction result.

    Map<String, Object> inputMap = new HashMap<>();
    Expression input =;
    PredictiveIndex index = IndexBuilder.predictiveIndex("ImageClassifier", input, null);
    database.createIndex("predictive-index-image-classifier", index);

    Run a Prediction Query

    The code below creates a query that calls the prediction function to return the "label" value for the first 10 results in the database.

    Map<String, Object> inputProperties = new HashMap<>();
    Expression input =;
    PredictionFunction prediction = PredictiveModel.predict("ImageClassifier", input); (1)
    Query query = QueryBuilder
    // Run the query.
    ResultSet result = query.execute();
    Log.d(TAG, "Number of rows: " + result.allResults().size());
    1 The PredictiveModel.predict() method returns a constructed Prediction Function object which can be used further to specify a property value extracted from the output dictionary of the PredictiveModel.predict() function.
    The null value returned by the prediction method will be interpreted as MISSING value in queries.

    Unregister the Model

    To unregister the model you must call the Database.prediction.unregisterModel static method.

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