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$timeout

Functionality​

Definition​

The $timeout endpoint defines the number of seconds to save an entity set in the server's cache. This parameter works in conjunction with $method=entityset to control the lifespan of the cached entity set.

Syntax​

To set a timeout for an entity set, use the following format:

GET /rest/{{dataClass}}?$filter="{{filterExpression}}"&$method=entityset&?$timeout={{seconds}}
tip

The $timeout endpoint accepts a numerical value representing the number of seconds the entity set should remain in the cache. For example, 1800 seconds for 30 minutes.

Detailed Behavior​

Default Timeout​

By default, the timeout is set to two (2) hours.

Using the $timeout Parameter​

When an entity set is created with a specified timeout, the following occurs:

  • The entity set is stored in the cache for the defined number of seconds.

  • Each time the entity set is accessed, the timeout is recalculated from the current time.

  • If the entity set is recreated using $savedfilter, the new default timeout is 10 minutes.

Using Specific Formats​

To set different timeout durations for an entity set, adjust the number of seconds in the $timeout parameter.

Combining with $expand​

The $timeout parameter can be used alongside $expand to manage the lifespan of expanded entity sets. Ensure that the $expand parameter is properly defined to retrieve related entities within the specified timeout period.

Combining with Other Parameters​

The $timeout parameter can be combined with other parameters:

  • $expand: Retrieve related entities within the specified timeout period.

  • $filter: Define specific criteria for the entities included in the entity set.

  • $orderby: Sort the entities in the entity set.

  • $top/$limit: Limit the number of entities returned in the entity set.

  • $skip: Skip a specified number of entities in the result set.

  • $savedfilter and $savedorderby: Save the filter and order by criteria to recreate the entity set with the same reference ID.

Use Cases​

Setting a Custom Timeout​

Request:

To create an entity set that expires after 20 minutes:

GET /rest/Employee?$filter="salary>50000"&$method=entityset&$timeout=1200

Response:

{
    "__ENTITYSET": "/rest/Employee/$entityset/3BA2B71499244F60A38CD51E11ACDDF8",
    "__DATACLASS": "Employee",
    "__entityModel": "Employee",
    "__GlobalStamp": 0,
    "__COUNT": 50,
    "__SENT": 50,
    "__ENTITIES": [ ... ],
    "__FIRST": 0
}

Default Timeout Behavior​

If no $timeout parameter is specified, the default timeout of 2 hours is applied:

Request:

GET /rest/Employee?$filter="department='HR'"&$method=entityset

Response:

{
    "__ENTITYSET": "/rest/Employee/$entityset/3BA2B71499244F60A38CD51E11ACDDF8",
    "__DATACLASS": "Employee",
    "__entityModel": "Employee",
    "__GlobalStamp": 0,
    "__COUNT": 50,
    "__SENT": 50,
    "__ENTITIES": [ ... ],
    "__FIRST": 0
}

Accessing a Removed Entity Set​

Request:

GET /rest/Employee/$entityset/3BA2B71499244F60A38CD51E11ACDDF8

Response:

{
    "__ERROR": [
        {
            "message": "The \"3BA2B71499244F60A38CD51E11ACDDF8\" entity set cannot be found",
            "componentSignature": "dbmg",
            "errCode": 1802
        }
    ]
}

Recreating an Entity Set with $savedfilter​

If an entity set is removed and then recreated using $savedfilter, the timeout is reset to 10 minutes:

Request:

GET /rest/Employee?$filter="salary>50000"&$method=entityset&$savedfilter=true

Best Practices​

  • Set Appropriate Timeouts: Choose a timeout duration that balances performance and resource utilization.

  • Monitor Cache Usage: Regularly check the cache for expired or unused entity sets to optimize memory usage.

  • Handle Timeouts Gracefully: Implement logic to handle cases where the entity set may have expired or been removed from the cache.