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Mapping to Hazelcast Maps

Before you can query entries in maps, you need to create a mapping with the map connector so that the SQL service knows how to access the entries in the most efficient way.

What is the Map Connector

The map connector allows you to create mappings to a distributed map in a local Hazelcast cluster.

Installing the Connector

This connector is included in Hazelcast.

Map Security

If you use Hazelcast Enterprise, you can set up permissions to restrict clients' access to maps.

For example, to restrict reads on maps, you can use the create and read permissions. To restrict inserts, you can use the put permission.

For details, see Client Security.

Creating a Mapping to a Map

To create a mapping to a map in SQL, you must tell Hazelcast how to serialize/deserialize the keys and values by specifying the keyFormat and valueFormat options in the CREATE MAPPING statement.

For maps whose keys and values are primitives, you need to set these options to the SQL type that corresponds to the primitive:

  • keyFormat

  • valueFormat

For example, to create a mapping for IMap<Integer, String>:

CREATE MAPPING my_map
TYPE IMap
OPTIONS (
    'keyFormat'='int',
    'valueFormat'='varchar'
)

For a reference, see SQL Data Types.

For object formats, you must specify other options, depending on the serialization format:

Portable Objects

If your map’s keys or values are portable, you need to provide the following additional options:

  • keyPortableFactoryId/ valuePortableFactoryId

  • keyPortableClassId/ valuePortableClassId

  • keyPortableVersion/ valuePortableVersion (optional, default is 0)

For example, to create a mapping for a map where both key and value are portable:

CREATE MAPPING my_map
TYPE IMap
OPTIONS (
    'keyFormat' = 'portable',
    'keyPortableFactoryId' = '123',
    'keyPortableClassId' = '456',
    'keyPortableVersion' = '0',  -- optional
    'valueFormat' = 'portable',
    'valuePortableFactoryId' = '123',
    'valuePortableClassId' = '789',
    'valuePortableVersion' = '0'  -- optional
)

If you omit a column list from the CREATE MAPPING statement, Hazelcast will resolve the column names and types by looking at the ClassDefinition found using the given factory ID, class ID, and version.

If the ClassDefinition with the given IDs is not known to the cluster, you must provide a column list so that Hazelcast can use it to create the ClassDefinition.

For more information about this serialization option, see Implementing Portable Serialization.

Compact Objects

If your map’s keys or values are compact, you need to provide the following additional options:

  • keyCompactTypeName

  • valueCompactTypeName

The column list is mandatory and Hazelcast will create the Compact objects schema based on the column list.

The benefit of this format is that it doesn’t deserialize the whole key or value when reading only a subset of fields. Also it doesn’t require a custom Java class to be defined on the cluster, so it’s usable for non-Java clients similar to Portable. And it is more space-efficient than Portable.

Example mapping where both key and value are Compact:

CREATE MAPPING my_map (
	id INT EXTERNAL NAME "__key.id",
	name VARCHAR,
	surname VARCHAR,
	age INT)
TYPE IMap
OPTIONS (
    'keyFormat' = 'compact',
    'keyCompactTypeName' = 'personId',
    'valueFormat' = 'compact',
    'valueCompactTypeName' = 'person',
)

For more information about this serialization option, see Compact Serialization (BETA).

JSON Objects

For maps whose values are stored in JSON, you must declare the field names in the column list.

For example, to create a mapping for a map whose values are JSON objects with the ticker and amount fields:

CREATE MAPPING my_map(
    __key BIGINT,
    ticker VARCHAR,
    amount INT)
TYPE IMap
OPTIONS (
    'keyFormat' = 'bigint',
    'valueFormat' = 'json-flat')

There are no additional options for this format.

By default, Hazelcast serializes JSON into HazelcastJsonValue objects, which allows you to query its fields.

JSON’s type system doesn’t match SQL’s exactly. For example, JSON numbers have unlimited precision, but such numbers are typically not portable. We convert SQL integer and floating-point types into JSON numbers. We convert the DECIMAL type, as well as all temporal types, to JSON strings.

Hazelcast doesn’t yet support the JSON type from the SQL standard. As a result, you can’t use functions like JSON_VALUE or JSON_QUERY.

Java Objects

For maps whose keys or values are serialized with Java serialization, DataSerializable or IdentifiedDataSerializable, you need to provide the name of the Java class into which you want to serialize data, using the following additional options:

  • 'keyJavaClass'

  • 'valueJavaClass'

For example:

CREATE MAPPING my_map
TYPE IMap
OPTIONS (
    'keyFormat' = 'java',
    'keyJavaClass' = 'java.lang.Long',
    'valueFormat' = 'java',
    'valueJavaClass' = 'com.example.Person')

If the Java class corresponds to one of the basic data types (numbers, dates, strings), that type will be used for the key or value and mapped as a column named __key for keys and this for values. In the example above, the key will be mapped with the BIGINT type. In fact, the above keyFormat and keyJavaClass duo is equivalent to 'keyFormat'='bigint'.

If the Java class is not one of the basic types:

  • Hazelcast will analyze the class using reflection and use its properties as column names.

    Hazelcast recognizes public fields and JavaBean-style getters. If some property has a non-primitive type, it will be mapped under the OBJECT type.

  • The class must be available to the cluster.

    You can either add the class to the members' classpaths by creating a JAR file and adding it to the lib directory, or you can use user code deployment. User code deployment must be enabled on the members, see Deploying User Code from Clients for details.