ApsaraDB for MongoDB:Compatibility details of DynamoDB-compatible ApsaraDB for MongoDB instances

Background information

Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability. ApsaraDB for MongoDB is compatible with the DynamoDB protocol. You can select the DynamoDB protocol to create a DynamoDB-compatible ApsaraDB for MongoDB instance. For more information about how to create a DynamoDB-compatible instance, see Create a DynamoDB-compatible ApsaraDB for MongoDB instance.

Precautions

• The DynamoDB protocol is supported only for ApsaraDB for MongoDB sharded cluster instances that run MongoDB 4.0.
• You can modify the protocol type to DynamoDB for existing ApsaraDB for MongoDB sharded cluster instances to make them compatible with the DynamoDB protocol.
• The DynamoDB protocol is supported only for ApsaraDB for MongoDB sharded cluster instances that use the VPC network type. No authentication is required.

Compatibility details of DynamoDB operations

Compatibility details of DynamoDB Streams operations

Data structures of DynamoDB operations

Compatibility details of expressions

• An attribute name that contains .: An attribute name that contains . indicates a scalar attribute or a nested document. In Amazon DynamoDB, if an expression attribute name maps to all elements in a document path, the attribute is handled as a scalar attribute. Otherwise, the attribute is handled as a nested attribute.
  Note Scalar attributes that contain . such as a query or projection expression cannot be processed in ApsaraDB for MongoDB.
• Projection expressions: support only one-dimensional arrays. When a projection expression contains only one array element, other fields are returned.
• Condition expressions:
  • Syntax for condition expressions in Amazon DynamoDB:

    condition-expression ::=
          operand comparator operand
        | operand BETWEEN operand AND operand
        | operand IN ( operand (',' operand (, ...) ))
        | function
        | condition AND condition
        | condition OR condition
        | NOT condition
        | ( condition )
    
    comparator ::=
        =
        | <>
        | <
        | <=
        | >
        | >=
    
    function ::=
        attribute_exists (path)
        | attribute_not_exists (path)
        | attribute_type (path, type)
        | begins_with (path, substr)
        | contains (path, operand)
        | size (path)

  • In operand1 comparator operand2, operand1 must be a path and operand2 must be an expression attribute value.
  • In operand1 BETWEEN operand2 AND operand3, operand1 must be a path, and other operand must be expression attribute values.
  • In operand1 IN ( operand2 (',' operand3 (, ...) )), the operand1 must be a path and other operand must be expression attribute values.
  • For the size(path) function in function, the path field must be of the STRING type (used to determine the length) or of the SET or LIST type (used to determine the size). It cannot be of the BINARY or MAP type.
• Update expressions:
  • Syntax for update expressions in Amazon DynamoDB:

    update-expression ::=
        [ SET action [, action] ... ]
        [ REMOVE action [, action] ...]
        [ ADD action [, action] ... ]
        [ DELETE action [, action] ...]
    
    set-action ::=
        path = value
    
    value ::=
        operand
        | operand '+' operand
        | operand '-' operand
    
    operand ::=
        path | function
    
    function ::=
        if_not_exists (path, value)
        | list_append (list1, list2)
    
    remove-action ::=
        path
    
    add-action ::=
        path value
    
    delete-action ::=
        path value

  • set-action:
    • In SET path = operand, operand cannot be a path.
    • In SET path = operand1 '+'|'-' operand2, operand1 must be a path. This indicates that only field increment or decrement is supported in this expression.
    • In SET path = if_not_exists (path, value), two paths must be equal, and valuemust be an expression attribute value.
    • In SET path = if_not_exists (path, value), partial updates are not supported when multiple conditions are concurrently specified. This indicates that all conditions must be met for this expression to be executed.
    • In SET path = list_append(list1, list2), one of the list1 and list2 values must be equal to path, and the other one must be an expression attribute value.
  • remove-action: When an element in a list is removed, null is used to replace the removed element. The List size remains unchanged and the remaining elements are not shifted.

Data type mappings

Amazon DynamoDB supports differ data types from ApsarsDB for MongoDB. Data type mappings are provided between DynamoDB-compatible ApsaraDB for MongoDB instances and ApsaraDB for MongoDB instances for compatibility between the two sets of data types.