.. Licensed under the Apache License, Version 2.0 (the "License"); you may not .. use this file except in compliance with the License. You may obtain a copy of .. the License at .. .. http://www.apache.org/licenses/LICENSE-2.0 .. .. Unless required by applicable law or agreed to in writing, software .. distributed under the License is distributed on an "AS IS" BASIS, WITHOUT .. WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the .. License for the specific language governing permissions and limitations under .. the License. .. _api/db/changes: ================ ``/db/_changes`` ================ .. http:get:: /{db}/_changes :synopsis: Returns changes for the given database Returns a sorted list of changes made to documents in the database, in time order of application, can be obtained from the database's ``_changes`` resource. Only the most recent change for a given document is guaranteed to be provided, for example if a document has had fields added, and then deleted, an API client checking for changes will not necessarily receive the intermediate state of added documents. This can be used to listen for update and modifications to the database for post processing or synchronization, and for practical purposes, a continuously connected ``_changes`` feed is a reasonable approach for generating a real-time log for most applications. :param db: Database name :
` filter. Since `length of URL is limited`_, it is better to use :post:`/{db}/_changes` instead. :query boolean conflicts: Includes `conflicts` information in response. Ignored if `include_docs` isn't ``true``. Default is ``false``. :query boolean descending: Return the change results in descending sequence order (most recent change first). Default is ``false``. :query string feed: - **normal** Specifies :ref:`Normal Polling Mode `. All past changes are returned immediately. *Default.* - **longpoll** Specifies :ref:`Long Polling Mode `. Waits until at least one change has occurred, sends the change, then closes the connection. Most commonly used in conjunction with ``since=now``, to wait for the next change. - **continuous** Sets :ref:`Continuous Mode `. Sends a line of JSON per event. Keeps the socket open until ``timeout``. - **eventsource** Sets :ref:`Event Source Mode `. Works the same as Continuous Mode, but sends the events in `EventSource `_ format. :query string filter: Reference to a :ref:`filter function ` from a design document that will filter whole stream emitting only filtered events. See the section `Change Notifications in the book CouchDB The Definitive Guide`_ for more information. :query number heartbeat: Period in *milliseconds* after which an empty line is sent in the results. Only applicable for :ref:`longpoll `, :ref:`continuous `, and :ref:`eventsource ` feeds. Overrides any timeout to keep the feed alive indefinitely. Default is ``60000``. May be ``true`` to use default value. :query boolean include_docs: Include the associated document with each result. If there are conflicts, only the winning revision is returned. Default is ``false``. :query boolean attachments: Include the Base64-encoded content of :ref:`attachments ` in the documents that are included if ``include_docs`` is ``true``. Ignored if ``include_docs`` isn't ``true``. Default is ``false``. :query boolean att_encoding_info: Include encoding information in attachment stubs if ``include_docs`` is ``true`` and the particular attachment is compressed. Ignored if ``include_docs`` isn't ``true``. Default is ``false``. :query number last-event-id: Alias of `Last-Event-ID` header. :query number limit: Limit number of result rows to the specified value (note that using ``0`` here has the same effect as ``1``). :query since: Start the results from the change immediately after the given update sequence. Can be valid update sequence or ``now`` value. Default is ``0``. :query string style: Specifies how many revisions are returned in the changes array. The default, ``main_only``, will only return the current "winning" revision; ``all_docs`` will return all leaf revisions (including conflicts and deleted former conflicts). :query number timeout: Maximum period in *milliseconds* to wait for a change before the response is sent, even if there are no results. Only applicable for :ref:`longpoll ` or :ref:`continuous ` feeds. Default value is specified by :config:option:`chttpd/changes_timeout` configuration option. Note that ``60000`` value is also the default maximum timeout to prevent undetected dead connections. :query string view: Allows to use view functions as filters. Documents counted as "passed" for view filter in case if map function emits at least one record for them. See :ref:`changes/filter/view` for more info. :query number seq_interval: When fetching changes in a batch, setting the *seq_interval* parameter tells CouchDB to only calculate the update seq with every Nth result returned. By setting **seq_interval=** , where ```` is the number of results requested per batch, load can be reduced on the source CouchDB database; computing the seq value across many shards (esp. in highly-sharded databases) is expensive in a heavily loaded CouchDB cluster. :>header Cache-Control: ``no-cache`` if changes feed is :ref:`eventsource ` :>header Content-Type: - :mimetype:`application/json` - :mimetype:`text/event-stream` - :mimetype:`text/plain; charset=utf-8` :>header ETag: Response hash if changes feed is `normal` :>header Transfer-Encoding: ``chunked`` :>json json last_seq: Last change update sequence :>json number pending: Count of remaining items in the feed :>json array results: Changes made to a database :code 200: Request completed successfully :code 400: Bad request The ``results`` field of database changes: :json array changes: List of document's leaves with single field ``rev``. :json string id: Document ID. :json json seq: Update sequence. :json bool deleted: ``true`` if the document is deleted. **Request**: .. code-block:: http GET /db/_changes?style=all_docs HTTP/1.1 Accept: application/json Host: localhost:5984 **Response**: .. code-block:: http HTTP/1.1 200 OK Cache-Control: must-revalidate Content-Type: application/json Date: Mon, 12 Aug 2013 00:54:58 GMT ETag: "6ASLEKEMSRABT0O5XY9UPO9Z" Server: CouchDB (Erlang/OTP) Transfer-Encoding: chunked { "last_seq": "5-g1AAAAIreJyVkEsKwjAURZ-toI5cgq5A0sQ0OrI70XyppcaRY92J7kR3ojupaSPUUgotgRd4yTlwbw4A0zRUMLdnpaMkwmyF3Ily9xBwEIuiKLI05KOTW0wkV4rruP29UyGWbordzwKVxWBNOGMKZhertDlarbr5pOT3DV4gudUC9-MPJX9tpEAYx4TQASns2E24ucuJ7rXJSL1BbEgf3vTwpmedCZkYa7Pulck7Xt7x_usFU2aIHOD4eEfVTVA5KMGUkqhNZV-8_o5i", "pending": 0, "results": [ { "changes": [ { "rev": "2-7051cbe5c8faecd085a3fa619e6e6337" } ], "id": "6478c2ae800dfc387396d14e1fc39626", "seq": "3-g1AAAAG3eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MSGXAqSVIAkkn2IFUZzIkMuUAee5pRqnGiuXkKA2dpXkpqWmZeagpu_Q4g_fGEbEkAqaqH2sIItsXAyMjM2NgUUwdOU_JYgCRDA5ACGjQfn30QlQsgKvcjfGaQZmaUmmZClM8gZhyAmHGfsG0PICrBPmQC22ZqbGRqamyIqSsLAAArcXo" }, { "changes": [ { "rev": "3-7379b9e515b161226c6559d90c4dc49f" } ], "deleted": true, "id": "5bbc9ca465f1b0fcd62362168a7c8831", "seq": "4-g1AAAAHXeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBMZc4EC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HqQ_kQG3qgSQqnoUtxoYGZkZG5uS4NY8FiDJ0ACkgAbNx2cfROUCiMr9CJ8ZpJkZpaaZEOUziBkHIGbcJ2zbA4hKsA-ZwLaZGhuZmhobYurKAgCz33kh" }, { "changes": [ { "rev": "6-460637e73a6288cb24d532bf91f32969" }, { "rev": "5-eeaa298781f60b7bcae0c91bdedd1b87" } ], "id": "729eb57437745e506b333068fff665ae", "seq": "5-g1AAAAIReJyVkE0OgjAQRkcwUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloRid3MMkEUoJHbXbOxVy6arc_SxQWQzRVHCuYHaxSpuj1aqbj0t-3-AlSrZakn78oeSvjRSIkIhSNiCFHbsKN3c50b02mURvEB-yD296eNOzzoRMRLRZ98rkHS_veGcC_nR-fGe1gaCaxihhjOI2lX0BhniHaA" } ] } .. _length of URL is limited: http://stackoverflow.com/a/417184/965635 .. versionchanged:: 0.11.0 added ``include_docs`` parameter .. versionchanged:: 1.2.0 added ``view`` parameter and special value `_view` for ``filter`` one .. versionchanged:: 1.3.0 ``since`` parameter could take `now` value to start listen changes since current seq number. .. versionchanged:: 1.3.0 ``eventsource`` feed type added. .. versionchanged:: 1.4.0 Support ``Last-Event-ID`` header. .. versionchanged:: 1.6.0 added ``attachments`` and ``att_encoding_info`` parameters .. versionchanged:: 2.0.0 update sequences can be any valid json object, added ``seq_interval`` .. note:: If the specified replicas of the shards in any given since value are unavailable, alternative replicas are selected, and the last known checkpoint between them is used. If this happens, you might see changes again that you have previously seen. Therefore, an application making use of the ``_changes`` feed should be ‘idempotent’, that is, able to receive the same data multiple times, safely. .. note:: Cloudant Sync and PouchDB already optimize the replication process by setting ``seq_interval`` parameter to the number of results expected per batch. This parameter increases throughput by reducing latency between sequential requests in bulk document transfers. This has resulted in up to a 20% replication performance improvement in highly-sharded databases. .. warning:: Using the ``attachments`` parameter to include attachments in the changes feed is not recommended for large attachment sizes. Also note that the Base64-encoding that is used leads to a 33% overhead (i.e. one third) in transfer size for attachments. .. warning:: The results returned by `_changes` are partially ordered. In other words, the order is not guaranteed to be preserved for multiple calls. .. http:post:: /{db}/_changes :synopsis: Returns changes for the given database for certain document IDs Requests the database changes feed in the same way as :get:`/{db}/_changes` does, but is widely used with ``?filter=_doc_ids`` query parameter and allows one to pass a larger list of document IDs to filter. **Request**: .. code-block:: http POST /recipes/_changes?filter=_doc_ids HTTP/1.1 Accept: application/json Content-Length: 40 Content-Type: application/json Host: localhost:5984 { "doc_ids": [ "SpaghettiWithMeatballs" ] } **Response**: .. code-block:: http HTTP/1.1 200 OK Cache-Control: must-revalidate Content-Type: application/json Date: Sat, 28 Sep 2013 07:23:09 GMT ETag: "ARIHFWL3I7PIS0SPVTFU6TLR2" Server: CouchDB (Erlang OTP) Transfer-Encoding: chunked { "last_seq": "5-g1AAAAIreJyVkEsKwjAURZ-toI5cgq5A0sQ0OrI70XyppcaRY92J7kR3ojupaSPUUgotgRd4yTlwbw4A0zRUMLdnpaMkwmyF3Ily9xBwEIuiKLI05KOTW0wkV4rruP29UyGWbordzwKVxWBNOGMKZhertDlarbr5pOT3DV4gudUC9-MPJX9tpEAYx4TQASns2E24ucuJ7rXJSL1BbEgf3vTwpmedCZkYa7Pulck7Xt7x_usFU2aIHOD4eEfVTVA5KMGUkqhNZV8_o5i", "pending": 0, "results": [ { "changes": [ { "rev": "13-bcb9d6388b60fd1e960d9ec4e8e3f29e" } ], "id": "SpaghettiWithMeatballs", "seq": "5-g1AAAAIReJyVkE0OgjAQRkcwUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloRid3MMkEUoJHbXbOxVy6arc_SxQWQzRVHCuYHaxSpuj1aqbj0t-3-AlSrZakn78oeSvjRSIkIhSNiCFHbsKN3c50b02mURvEB-yD296eNOzzoRMRLRZ98rkHS_veGcC_nR-fGe1gaCaxihhjOI2lX0BhniHaA" } ] } .. _changes: Changes Feeds ============= .. _changes/normal: Polling ------- By default all changes are immediately returned within the JSON body:: GET /somedatabase/_changes HTTP/1.1 .. code-block:: javascript {"results":[ {"seq":"1-g1AAAAF9eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P__7MSGXAqSVIAkkn2IFUZzIkMuUAee5pRqnGiuXkKA2dpXkpqWmZeagpu_Q4g_fGEbEkAqaqH2sIItsXAyMjM2NgUUwdOU_JYgCRDA5ACGjQfn30QlQsgKvcTVnkAovI-YZUPICpBvs0CAN1eY_c","id":"fresh","changes":[{"rev":"1-967a00dff5e02add41819138abb3284d"}]}, {"seq":"3-g1AAAAG3eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MSGXAqSVIAkkn2IFUZzIkMuUAee5pRqnGiuXkKA2dpXkpqWmZeagpu_Q4g_fGEbEkAqaqH2sIItsXAyMjM2NgUUwdOU_JYgCRDA5ACGjQfn30QlQsgKvcjfGaQZmaUmmZClM8gZhyAmHGfsG0PICrBPmQC22ZqbGRqamyIqSsLAAArcXo","id":"updated","changes":[{"rev":"2-7051cbe5c8faecd085a3fa619e6e6337CFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloRid3MMkEUoJHbXbOxVy6arc_SxQWQzRVHCuYHaxSpuj1aqbj0t-3-AlSrZakn78oeSvjRSIkIhSNiCFHbsKN3c50b02mURvEB-yD296eNOzzoRMRLRZ98rkHS_veGcC_nR-fGe1gaCaxihhjOI2lX0BhniHaA","id":"deleted","changes":[{"rev":"2-eec205a9d413992850a6e32678485900"}],"deleted":true} ], "last_seq":"5-g1AAAAIreJyVkEsKwjAURZ-toI5cgq5A0sQ0OrI70XyppcaRY92J7kR3ojupaSPUUgotgRd4yTlwbw4A0zRUMLdnpaMkwmyF3Ily9xBwEIuiKLI05KOTW0wkV4rruP29UyGWbordzwKVxWBNOGMKZhertDlarbr5pOT3DV4gudUC9-MPJX9tpEAYx4TQASns2E24ucuJ7rXJSL1BbEgf3vTwpmedCZkYa7Pulck7Xt7x_usFU2aIHOD4eEfVTVA5KMGUkqhNZV-8_o5i", "pending": 0} ``results`` is the list of changes in sequential order. New and changed documents only differ in the value of the rev; deleted documents include the ``"deleted": true`` attribute. (In the ``style=all_docs mode``, deleted applies only to the current/winning revision. The other revisions listed might be deleted even if there is no deleted property; you have to ``GET`` them individually to make sure.) ``last_seq`` is the update sequence of the last update returned (Equivalent to the last item in the results). Sending a ``since`` param in the query string skips all changes up to and including the given update sequence: .. code-block:: http GET /somedatabase/_changes?since=4-g1AAAAHXeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBMZc4EC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HqQ_kQG3qgSQqnoUtxoYGZkZG5uS4NY8FiDJ0ACkgAbNx2cfROUCiMr9CJ8ZpJkZpaaZEOUziBkHIGbcJ2zbA4hKsA-ZwLaZGhuZmhobYurKAgCz33kh HTTP/1.1 The return structure for ``normal`` and ``longpoll`` modes is a JSON array of changes objects, and the last update sequence. In the return format for ``continuous`` mode, the server sends a ``CRLF`` (carriage-return, linefeed) delimited line for each change. Each line contains the `JSON object` described above. You can also request the full contents of each document change (instead of just the change notification) by using the ``include_docs`` parameter. .. code-block:: javascript { "last_seq": "5-g1AAAAIreJyVkEsKwjAURZ-toI5cgq5A0sQ0OrI70XyppcaRY92J7kR3ojupaSPUUgotgRd4yTlwbw4A0zRUMLdnpaMkwmyF3Ily9xBwEIuiKLI05KOTW0wkV4rruP29UyGWbordzwKVxWBNOGMKZhertDlarbr5pOT3DV4gudUC9-MPJX9tpEAYx4TQASns2E24ucuJ7rXJSL1BbEgf3vTwpmedCZkYa7Pulck7Xt7x_usFU2aIHOD4eEfVTVA5KMGUkqhNZV-8_o5i", "pending": 0, "results": [ { "changes": [ { "rev": "2-eec205a9d413992850a6e32678485900" } ], "deleted": true, "id": "deleted", "seq": "5-g1AAAAIReJyVkE0OgjAQRkcwUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloRid3MMkEUoJHbXbOxVy6arc_SxQWQzRVHCuYHaxSpuj1aqbj0t-3-AlSrZakn78oeSvjRSIkIhSNiCFHbsKN3c50b02mURvEByD296eNOzzoRMRLRZ98rkHS_veGcC_nR-fGe1gaCaxihhjOI2lX0BhniHaA", } ] } .. _changes/longpoll: Long Polling ------------ The `longpoll` feed, probably most applicable for a browser, is a more efficient form of polling that waits for a change to occur before the response is sent. `longpoll` avoids the need to frequently poll CouchDB to discover nothing has changed! The request to the server will remain open until a change is made on the database and is subsequently transferred, and then the connection will close. This is low load for both server and client. The response is basically the same JSON as is sent for the `normal` feed. Because the wait for a change can be significant you can set a timeout before the connection is automatically closed (the ``timeout`` argument). You can also set a heartbeat interval (using the ``heartbeat`` query argument), which sends a newline to keep the connection active. Keep in mind that ``heartbeat`` means "Send a linefeed every ``x`` ms if no change arrives, and hold the connection indefinitely" while ``timeout`` means "Hold this connection open for ``x`` ms, and if no change arrives in that time, close the socket." ``heartbeat`` overrides ``timeout``. .. _changes/continuous: Continuous ---------- Continually polling the CouchDB server is not ideal - setting up new HTTP connections just to tell the client that nothing happened puts unnecessary strain on CouchDB. A continuous feed stays open and connected to the database until explicitly closed and changes are sent to the client as they happen, i.e. in near real-time. As with the `longpoll` feed type you can set both the timeout and heartbeat intervals to ensure that the connection is kept open for new changes and updates. Keep in mind that ``heartbeat`` means "Send a linefeed every ``x`` ms if no change arrives, and hold the connection indefinitely" while ``timeout`` means "Hold this connection open for ``x`` ms, and if no change arrives in that time, close the socket." ``heartbeat`` overrides ``timeout``. The continuous feed's response is a little different than the other feed types to simplify the job of the client - each line of the response is either empty or a JSON object representing a single change, as found in the normal feed's results. If `limit` has been specified the feed will end with a `{ last_seq }` object. .. code-block:: http GET /somedatabase/_changes?feed=continuous HTTP/1.1 .. code-block:: javascript {"seq":"1-g1AAAAF9eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MSGXAqSVIAkkn2IFUZzIkMuUAee5pRqnGiuXkKA2dpXkpqWmZeagpu_Q4g_fGEbEkAqaqH2sIItsXAyMjM2NgUUwdOU_JYgCRDA5ACGjQfn30QlQsgKvcTVnkAovI-YZUPICpBvs0CAN1eY_c","id":"fresh","changes":[{"rev":"5-g1AAAAHxeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D666H6GcH6DYyMzIyNTUnwRR4LkGRoAFJAg-YjwiMtOdXCwJyU8ICYtABi0n6EnwzSzIxS00yI8hPEjAMQM-5nJTIQUPkAovI_UGUWAA0SgOI","id":"updated","changes":[{"rev":"2-7051cbe5c8faecd085a3fa619e6e6337"}]} {"seq":"3-g1AAAAHReJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D660H6ExlwqspjAZIMDUAKqHA-yCZGiEuTUy0MzEnxL8SkBRCT9iPcbJBmZpSaZkKUmyFmHICYcZ-wux9AVIJ8mAUABgp6XQ","id":"deleted","changes":[{"rev":"2-eec205a9d413992850a6e32678485900"}],"deleted":true} ... tum tee tum ... {"seq":"6-g1AAAAIreJyVkEsKwjAURWMrqCOXoCuQ9MU0OrI70XyppcaRY92J7kR3ojupaVNopRQsgRd4yTlwb44QmqahQnN7VjpKImAr7E6Uu4eAI7EoiiJLQx6c3GIiuVJcx93vvQqxdFPsaguqLAY04YwpNLtYpc3RatXPJyW__-EFllst4D_-UPLXmh9VPAaICaEDUtixm-jmLie6N30YqTeYDenDmx7e9GwyYRODNuu_MnnHyzverV6AMkPkAMfHO1rdUAKUkqhLZV-_0o5j","id":"updated","changes":[{"rev":"3-825cb35de44c433bfb2df415563a19de"}]} Obviously, `... tum tee tum ...` does not appear in the actual response, but represents a long pause before the change with seq 6 occurred. .. _Change Notifications in the book CouchDB The Definitive Guide: http://guide.couchdb.org/draft/notifications.html .. _changes/eventsource: Event Source ------------ The `eventsource` feed provides push notifications that can be consumed in the form of DOM events in the browser. Refer to the `W3C eventsource specification`_ for further details. CouchDB also honours the ``Last-Event-ID`` parameter. .. code-block:: http GET /somedatabase/_changes?feed=eventsource HTTP/1.1 .. code-block:: javascript // define the event handling function if (window.EventSource) { var source = new EventSource("/somedatabase/_changes?feed=eventsource"); source.onerror = function(e) { alert('EventSource failed.'); }; var results = []; var sourceListener = function(e) { var data = JSON.parse(e.data); results.push(data); }; // start listening for events source.addEventListener('message', sourceListener, false); // stop listening for events source.removeEventListener('message', sourceListener, false); } If you set a heartbeat interval (using the ``heartbeat`` query argument), CouchDB will send a ``hearbeat`` event that you can subscribe to with: .. code-block:: javascript source.addEventListener('heartbeat', function () {}, false); This can be monitored by the client application to restart the EventSource connection if needed (i.e. if the TCP connection gets stuck in a half-open state). .. note:: EventSource connections are subject to cross-origin resource sharing restrictions. You might need to configure :ref:`CORS support ` to get the EventSource to work in your application. .. _W3C eventsource specification: http://www.w3.org/TR/eventsource/ .. _changes/filter: Filtering ========= You can filter the contents of the changes feed in a number of ways. The most basic way is to specify one or more document IDs to the query. This causes the returned structure value to only contain changes for the specified IDs. Note that the value of this query argument should be a JSON formatted array. You can also filter the ``_changes`` feed by defining a filter function within a design document. The specification for the filter is the same as for replication filters. You specify the name of the filter function to the ``filter`` parameter, specifying the design document name and :ref:`filter name `. For example: .. code-block:: http GET /db/_changes?filter=design_doc/filtername HTTP/1.1 Additionally, a couple of built-in filters are available and described below. .. _changes/filter/doc_ids: _doc_ids -------- This filter accepts only changes for documents which ID in specified in ``doc_ids`` query parameter or payload's object array. See :post:`/{db}/_changes` for an example. .. _changes/filter/selector: _selector --------- .. versionadded:: 2.0 This filter accepts only changes for documents which match a specified selector, defined using the same :ref:`selector syntax ` used for :ref:`_find `. This is significantly more efficient than using a JavaScript filter function and is the recommended option if filtering on document attributes only. Note that, unlike JavaScript filters, selectors do not have access to the request object. **Request**: .. code-block:: http POST /recipes/_changes?filter=_selector HTTP/1.1 Content-Type: application/json Host: localhost:5984 { "selector": { "_id": { "$regex": "^_design/" } } } **Response**: .. code-block:: http HTTP/1.1 200 OK Cache-Control: must-revalidate Content-Type: application/json Date: Tue, 06 Sep 2016 20:03:23 GMT Etag: "1H8RGBCK3ABY6ACDM7ZSC30QK" Server: CouchDB (Erlang OTP/18) Transfer-Encoding: chunked { "last_seq": "11-g1AAAAIreJyVkEEKwjAQRUOrqCuPoCeQZGIaXdmbaNIk1FLjyrXeRG-iN9Gb1LQRaimFlsAEJnkP_s8RQtM0VGhuz0qTmABfYXdI7h4CgeSiKIosDUVwcotJIpQSOmp_71TIpZty97OgymJAU8G5QrOLVdocrVbdfFzy-wYvcbLVEvrxh5K_NlJggIhSNiCFHbmJbu5yonttMoneYD6kD296eNOzzoRNBNqse2Xyjpd3vP96AcYNTQY4Pt5RdTOuHIwCY5S0qewLwY6OaA", "pending": 0, "results": [ { "changes": [ { "rev": "10-304cae84fd862832ea9814f02920d4b2" } ], "id": "_design/ingredients", "seq": "8-g1AAAAHxeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D666H6GcH6DYyMzIyNTUnwRR4LkGRoAFJAg-ZnJTIQULkAonI_ws0GaWZGqWkmRLkZYsYBiBn3Cdv2AKIS7ENWsG2mxkampsaGmLqyAOYpgEo" }, { "changes": [ { "rev": "123-6f7c1b7c97a9e4f0d22bdf130e8fd817" } ], "deleted": true, "id": "_design/cookbook", "seq": "9-g1AAAAHxeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D661F8YWBkZGZsbEqCL_JYgCRDA5ACGjQ_K5GBgMoFEJX7EW42SDMzSk0zIcrNEDMOQMy4T9i2BxCVYB-ygm0zNTYyNTU2xNSVBQDnK4BL" }, { "changes": [ { "rev": "6-5b8a52c22580e922e792047cff3618f3" } ], "deleted": true, "id": "_design/meta", "seq": "11-g1AAAAIReJyVkE0OgjAQRiegUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloQhO7mGSCKWEjtrtnQq5dFXufhaoLIZoKjhXMLtYpc3RatXNxyW_b_ASJVstST_-UPLXRgpESEQpG5DCjlyFm7uc6F6bTKI3iA_Zhzc9vOlZZ0ImItqse2Xyjpd3vDMBfzo_vrPawLiaxihhjOI2lX0BirqHbg" } ] } .. _changes/filter/selector/missing: Missing selector ################ If the selector object is missing from the request body, the error message is similar to the following example: .. code-block:: json { "error": "bad request", "reason": "Selector must be specified in POST payload" } .. _changes/filter/selector/invalidjson: Not a valid JSON object ####################### If the selector object is not a well-formed JSON object, the error message is similar to the following example: .. code-block:: json { "error": "bad request", "reason": "Selector error: expected a JSON object" } .. _changes/filter/selector/invalidselector: Not a valid selector #################### If the selector object does not contain a valid selection expression, the error message is similar to the following example: .. code-block:: json { "error": "bad request", "reason": "Selector error: expected a JSON object" } .. _changes/filter/design: _design ------- The ``_design`` filter accepts only changes for any design document within the requested database. **Request**: .. code-block:: http GET /recipes/_changes?filter=_design HTTP/1.1 Accept: application/json Host: localhost:5984 **Response**: .. code-block:: http HTTP/1.1 200 OK Cache-Control: must-revalidate Content-Type: application/json Date: Tue, 06 Sep 2016 12:55:12 GMT ETag: "ARIHFWL3I7PIS0SPVTFU6TLR2" Server: CouchDB (Erlang OTP) Transfer-Encoding: chunked { "last_seq": "11-g1AAAAIreJyVkEEKwjAQRUOrqCuPoCeQZGIaXdmbaNIk1FLjyrXeRG-iN9Gb1LQRaimFlsAEJnkP_s8RQtM0VGhuz0qTmABfYXdI7h4CgeSiKIosDUVwcotJIpQSOmp_71TIpZty97OgymJAU8G5QrOLVdocrVbdfFzy-wYvcbLVEvrxh5K_NlJggIhSNiCFHbmJbu5yonttMoneYD6kD296eNOzzoRNBNqse2Xyjpd3vP96AcYNTQY4Pt5RdTOuHIwCY5S0qewLwY6OaA", "pending": 0, "results": [ { "changes": [ { "rev": "10-304cae84fd862832ea9814f02920d4b2" } ], "id": "_design/ingredients", "seq": "8-g1AAAAHxeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D666H6GcH6DYyMzIyNTUnwRR4LkGRoAFJAg-ZnJTIQULkAonI_ws0GaWZGqWkmRLkZYsYBiBn3Cdv2AKIS7ENWsG2mxkampsaGmLqyAOYpgEo" }, { "changes": [ { "rev": "123-6f7c1b7c97a9e4f0d22bdf130e8fd817" } ], "deleted": true, "id": "_design/cookbook", "seq": "9-g1AAAAHxeJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBOZcoEC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HkV_kkGyZWqSEXH6E0D661F8YWBkZGZsbEqCL_JYgCRDA5ACGjQ_K5GBgMoFEJX7EW42SDMzSk0zIcrNEDMOQMy4T9i2BxCVYB-ygm0zNTYyNTU2xNSVBQDnK4BL" }, { "changes": [ { "rev": "6-5b8a52c22580e922e792047cff3618f3" } ], "deleted": true, "id": "_design/meta", "seq": "11-g1AAAAIReJyVkE0OgjAQRiegUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloQhO7mGSCKWEjtrtnQq5dFXufhaoLIZoKjhXMLtYpc3RatXNxyW_b_ASJVstST_-UPLXRgpESEQpG5DCjlyFm7uc6F6bTKI3iA_Zhzc9vOlZZ0ImItqse2Xyjpd3vDMBfzo_vrPawLiaxihhjOI2lX0BirqHbg" } ] } .. _changes/filter/view: _view ----- .. versionadded:: 1.2 The special filter ``_view`` allows to use existing :ref:`map function ` as the :ref:`filter `. If the map function emits anything for the processed document it counts as accepted and the changes event emits to the feed. For most use-practice cases `filter` functions are very similar to `map` ones, so this feature helps to reduce amount of duplicated code. .. warning:: While :ref:`map functions ` doesn't process the design documents, using ``_view`` filter forces them to do this. You need to be sure, that they are ready to handle documents with *alien* structure without panic. .. note:: Using ``_view`` filter doesn't queries the view index files, so you cannot use common :ref:`view query parameters ` to additionally filter the changes feed by index key. Also, CouchDB doesn't returns the result instantly as it does for views - it really uses the specified map function as filter. Moreover, you cannot make such filters dynamic e.g. process the request query parameters or handle the :ref:`userctx_object` - the map function is only operates with the document. **Request**: .. code-block:: http GET /recipes/_changes?filter=_view&view=ingredients/by_recipe HTTP/1.1 Accept: application/json Host: localhost:5984 **Response**: .. code-block:: http HTTP/1.1 200 OK Cache-Control: must-revalidate Content-Type: application/json Date: Tue, 06 Sep 2016 12:57:56 GMT ETag: "ARIHFWL3I7PIS0SPVTFU6TLR2" Server: CouchDB (Erlang OTP) Transfer-Encoding: chunked { "last_seq": "11-g1AAAAIreJyVkEEKwjAQRUOrqCuPoCeQZGIaXdmbaNIk1FLjyrXeRG-iN9Gb1LQRaimFlsAEJnkP_s8RQtM0VGhuz0qTmABfYXdI7h4CgeSiKIosDUVwcotJIpQSOmp_71TIpZty97OgymJAU8G5QrOLVdocrVbdfFzy-wYvcbLVEvrxh5K_NlJggIhSNiCFHbmJbu5yonttMoneYD6kD296eNOzzoRNBNqse2Xyjpd3vP96AcYNTQY4Pt5RdTOuHIwCY5S0qewLwY6OaA", "results": [ { "changes": [ { "rev": "13-bcb9d6388b60fd1e960d9ec4e8e3f29e" } ], "id": "SpaghettiWithMeatballs", "seq": "11-g1AAAAIReJyVkE0OgjAQRiegUVceQU9g-mOpruQm2tI2SLCuXOtN9CZ6E70JFmpCCCFCmkyTdt6bfJMDwDQNFcztWWkcY8JXyB2cu49AgFwURZGloQhO7mGSCKWEjtrtnQq5dFXufhaoLIZoKjhXMLtYpc3RatXNxyW_b_ASJVstST_-UPLXRgpESEQpG5DCjlyFm7uc6F6bTKI3iA_Zhzc9vOlZZ0ImItqse2Xyjpd3vDMBfzo_vrPawLiaxihhjOI2lX0BirqHbg" } ] }