Package io.objectbox.query

Class Query<T>

  • Type Parameters:
    T - Entity class for which results are returned.
    All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable
    public class Query<T>
extends java.lang.Object
implements java.io.Closeable
    A repeatable Query returning the latest matching Objects.

    Use find() or related methods to fetch the latest results from the BoxStore.

    Use property(Property) to only return values or an aggregate of a single Property.

    Make sure to close() this query once done with it to reclaim resources immediately.

    See the Queries documentation for details.

    • Method Detail

      • finalize

        protected void finalize()
                 throws java.lang.Throwable
        Explicitly call close() instead to avoid expensive finalization.
        Overrides:
        finalize in class java.lang.Object
        Throws:
        java.lang.Throwable

      • close

        public void close()
        Closes this query and frees used resources.

        If possible, call this always once done with this. Otherwise, will be called once this is finalized (e.g. garbage collected).

        Calling any other methods of this afterwards will throw an IllegalStateException.

        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable

      • copy

        public Query<T> copy()
        Creates a copy of this for use in another thread.

        Clones the native query, keeping any previously set parameters.

        Closing the original query does not close the copy. close() the copy once finished using it.

        Note: a set filter or sort order must be thread safe.

      • findFirst

        @Nullable
public T findFirst()
        Find the first Object matching the query.

      • findUnique

        @Nullable
public T findUnique()
        If there is a single matching object, returns it. If there is more than one matching object, throws NonUniqueResultException. If there are no matches returns null.

      • find

        @Nonnull
public java.util.List<T> find()
        Find all Objects matching the query.

      • find

        @Nonnull
public java.util.List<T> find​(long offset,
                              long limit)
        Find all Objects matching the query, skipping the first offset results and returning at most limit results. Use this for pagination.

      • findFirstId

        public long findFirstId()
        Returns the ID of the first matching object. If there are no results returns 0.

        Like findFirst(), but more efficient as no object is created.

        Ignores any query filter.

      • findUniqueId

        public long findUniqueId()
        If there is a single matching object, returns its ID. If there is more than one matching object, throws NonUniqueResultException. If there are no matches returns 0.

        Like findUnique(), but more efficient as no object is created.

        Ignores any query filter.

      • findIds

        @Nonnull
public long[] findIds()
        Very efficient way to get just the IDs without creating any objects. IDs can later be used to lookup objects (lookups by ID are also very efficient in ObjectBox).

        Note: a filter set with QueryBuilder.filter(QueryFilter) will be silently ignored!

      • findIds

        @Nonnull
public long[] findIds​(long offset,
                      long limit)
        Like findIds() but with a offset/limit param, e.g. for pagination.

        Note: a filter set with QueryBuilder.filter(QueryFilter) will be silently ignored!

      • findLazy

        @Nonnull
public LazyList<T> findLazy()
        Like findIds(), but wraps the Object IDs in an unmodifiable LazyList so Objects can be retrieved on demand. The LazyList does not cache retrieved Objects, so only basic List operations like getting or iterating list items are supported. See LazyList for details.

      • findLazyCached

        @Nonnull
public LazyList<T> findLazyCached()
        Like findIds(), but wraps the Object IDs in an unmodifiable, caching LazyList so Objects can be retrieved on demand. The LazyList caches retrieved Objects supporting almost all List operations, at the expense of used memory. See LazyList for details.

      • property

        public PropertyQuery property​(Property<T> property)
        Creates a PropertyQuery for the given property.

        A PropertyQuery uses the same conditions as this Query object, but returns only the value(s) of a single property (not an entity objects).

        Parameters:
        property - the property for which to return values

      • forEach

        public void forEach​(QueryConsumer<T> consumer)
        Emits query results one by one to the given consumer (synchronously). Once this method returns, the consumer will have received all result object). It "streams" each object from the database to the consumer, which is very memory efficient. Because this is run in a read transaction, the consumer gets a consistent view on the data. Like findLazy(), this method can be used for a high amount of data.

        Note: because the consumer is called within a read transaction it may not write to the database.

      • count

        public long count()
        Returns the count of Objects matching the query.

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             java.lang.String value)
        Sets a parameter previously given to the QueryBuilder to a new value.

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             long value)
        Sets a parameter previously given to the QueryBuilder to a new value.

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             double value)
        Sets a parameter previously given to the QueryBuilder to a new value.

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             java.util.Date value)
        Sets a parameter previously given to the QueryBuilder to a new value.
        Throws:
        java.lang.NullPointerException - if given date is null

      • setParameter

        public Query<T> setParameter​(java.lang.String alias,
                             java.util.Date value)
        Sets a parameter previously given to the QueryBuilder to a new value.
        Parameters:
        alias - as defined using QueryBuilder.parameterAlias(String).
        Throws:
        java.lang.NullPointerException - if given date is null

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             boolean value)
        Sets a parameter previously given to the QueryBuilder to a new value.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              long value1,
                              long value2)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              int[] values)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              long[] values)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              double value1,
                              double value2)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              java.lang.String[] values)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(Property<?> property,
                              java.lang.String key,
                              java.lang.String value)
        Sets a parameter previously given to the QueryBuilder to new values.

      • setParameters

        public Query<T> setParameters​(java.lang.String alias,
                              java.lang.String key,
                              java.lang.String value)
        Sets a parameter previously given to the QueryBuilder to new values.
        Parameters:
        alias - as defined using QueryBuilder.parameterAlias(String).

      • setParameter

        public Query<T> setParameter​(Property<?> property,
                             byte[] value)
        Sets a parameter previously given to the QueryBuilder to new values.

      • remove

        public long remove()
        Removes (deletes) all Objects matching the query
        Returns:
        count of removed Objects

      • subscribe

        public SubscriptionBuilder<java.util.List<T>> subscribe()
        A DataObserver can be subscribed to data changes using the returned builder. The observer is supplied via SubscriptionBuilder.observer(DataObserver) and will be notified once the query results have (potentially) changed.

        With subscribing, the observer will immediately get current query results. The query is run for the subscribing observer.

        Threading notes: Query observers are notified from a thread pooled. Observers may be notified in parallel. The notification order is the same as the subscription order, although this may not always be guaranteed in the future.

        Stale observers: you must hold on to the Query or DataSubscription objects to keep your DataObservers active. If this Query is not referenced anymore (along with its DataSubscriptions, which hold a reference to the Query internally), it may be GCed and observers may become stale (won't receive anymore data).

      • publish

        public void publish()
        Publishes the current data to all subscribed @DataObservers. This is useful triggering observers when new parameters have been set. Note, that setParameter methods will NOT be propagated to observers.

      • describe

        public java.lang.String describe()
        For logging and testing, returns a string describing this query like "Query for entity Example with 4 conditions with properties prop1, prop2".

        Note: the format of the returned string may change without notice.

      • describeParameters

        public java.lang.String describeParameters()
        For logging and testing, returns a string describing the conditions of this query like "(prop1 == A AND prop2 is null)".

        Note: the format of the returned string may change without notice.