HTTP Interface for Exporting Documents
Create export cursor
export all documents from a collection, using a cursor
A JSON object with these properties is required:
- count: boolean flag that indicates whether the number of documents in the result set should be returned in the "count" attribute of the result (optional). Calculating the "count" attribute might in the future have a performance impact so this option is turned off by default, and "count" is only returned when requested.
- fields (string): Contains an array of attribute names to include or exclude. Matching of attribute names for inclusion or exclusion will be done on the top level only. Specifying names of nested attributes is not supported at the moment.
- type: has to be be set to either include or exclude depending on which you want to use
- batchSize: maximum number of result documents to be transferred from the server to the client in one roundtrip (optional). If this attribute is not set, a server-controlled default value will be used.
- flush: if set to true, a WAL flush operation will be executed prior to the export. The flush operation will start copying documents from the WAL to the collection's datafiles. There will be an additional wait time of up to flushWait seconds after the flush to allow the WAL collector to change the adjusted document meta-data to point into the datafiles, too. The default value is false (i.e. no flush) so most recently inserted or updated documents from the collection might be missing in the export.
- flushWait: maximum wait time in seconds after a flush operation. The default value is 10. This option only has an effect when flush is set to true.
- limit: an optional limit value, determining the maximum number of documents to be included in the cursor. Omitting the limit attribute or setting it to 0 will lead to no limit being used. If a limit is used, it is undefined which documents from the collection will be included in the export and which will be excluded. This is because there is no natural order of documents in a collection.
- ttl: an optional time-to-live for the cursor (in seconds). The cursor will be removed on the server automatically after the specified amount of time. This is useful to ensure garbage collection of cursors that are not fully fetched by clients. If not set, a server-defined value will be used.
A call to this method creates a cursor containing all documents in the specified collection. In contrast to other data-producing APIs, the internal data structures produced by the export API are more lightweight, so it is the preferred way to retrieve all documents from a collection.
Documents are returned in a similar manner as in the
/_api/cursor REST API.
If all documents of the collection fit into the first batch, then no cursor
will be created, and the result object's hasMore attribute will be set to
false. If not all documents fit into the first batch, then the result
object's hasMore attribute will be set to true, and the id attribute
of the result will contain a cursor id.
The order in which the documents are returned is not specified.
By default, only those documents from the collection will be returned that are stored in the collection's datafiles. Documents that are present in the write-ahead log (WAL) at the time the export is run will not be exported.
To export these documents as well, the caller can issue a WAL flush request before calling the export API or set the flush attribute. Setting the flush option will trigger a WAL flush before the export so documents get copied from the WAL to the collection datafiles.
If the result set can be created by the server, the server will respond with HTTP 201. The body of the response will contain a JSON object with the result set.
The returned JSON object has the following properties:
error: boolean flag to indicate that an error occurred (false in this case)
code: the HTTP status code
result: an array of result documents (might be empty if the collection was empty)
hasMore: a boolean indicator whether there are more results available for the cursor on the server
count: the total number of result documents available (only available if the query was executed with the count attribute set)
id: id of temporary cursor created on the server (optional, see above)
If the JSON representation is malformed or the query specification is missing from the request, the server will respond with HTTP 400.
The body of the response will contain a JSON object with additional error details. The object has the following attributes:
error: boolean flag to indicate that an error occurred (true in this case)
code: the HTTP status code
errorNum: the server error number
errorMessage: a descriptive error message
Clients should always delete an export cursor result as early as possible because a lingering export cursor will prevent the underlying collection from being compacted or unloaded. By default, unused cursors will be deleted automatically after a server-defined idle time, and clients can adjust this idle time by setting the ttl value.
Note: this API is currently not supported on cluster coordinators.
- collection (required): The name of the collection to export.
201: is returned if the result set can be created by the server.
400: is returned if the JSON representation is malformed or the query specification is missing from the request.
404: The server will respond with HTTP 404 in case a non-existing collection is accessed in the query.
405: The server will respond with HTTP 405 if an unsupported HTTP method is used.
501: The server will respond with HTTP 501 if this API is called on a cluster coordinator.