.. 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. .. default-domain:: js .. _ddocs: ================ Design Documents ================ In this section we'll show how to write design documents, using the built-in :ref:`JavaScript Query Server `. But before we start to write our first document, let's take a look at the list of common objects that will be used during our code journey - we'll be using them extensively within each function: - :ref:`Database information object ` - :ref:`Request object ` - :ref:`Response object ` - :ref:`UserCtx object ` - :ref:`Database Security object ` - :ref:`Guide to JavaScript Query Server ` Creation and Structure ====================== Design documents contain functions such as view and update functions. These functions are executed when requested. Design documents are denoted by an id field with the format ``_design/{name}``. Their structure follows the example below. **Example**: .. code-block:: json { "_id": "_design/example", "views": { "view-number-one": { "map": "function (doc) {/* function code here - see below */}" }, "view-number-two": { "map": "function (doc) {/* function code here - see below */}", "reduce": "function (keys, values, rereduce) {/* function code here - see below */}" } }, "updates": { "updatefun1": "function(doc,req) {/* function code here - see below */}", "updatefun2": "function(doc,req) {/* function code here - see below */}" }, "filters": { "filterfunction1": "function(doc, req){ /* function code here - see below */ }" }, "validate_doc_update": "function(newDoc, oldDoc, userCtx, secObj) { /* function code here - see below */ }", "language": "javascript" } As you can see, a design document can include multiple functions of the same type. The example defines two views, both of which have a map function and one of which has a reduce function. It also defines two update functions and one filter function. The Validate Document Update function is a special case, as each design document cannot contain more than one of those. .. _viewfun: View Functions ============== Views are the primary tool used for querying and reporting on CouchDB databases. .. _mapfun: Map Functions ------------- .. function:: mapfun(doc) :param doc: The document that is being processed Map functions accept a single document as the argument and (optionally) :func:`emit` key/value pairs that are stored in a view. .. code-block:: javascript function (doc) { if (doc.type === 'post' && doc.tags && Array.isArray(doc.tags)) { doc.tags.forEach(function (tag) { emit(tag.toLowerCase(), 1); }); } } In this example a key/value pair is emitted for each value in the `tags` array of a document with a `type` of "post". Note that :func:`emit` may be called many times for a single document, so the same document may be available by several different keys. Also keep in mind that each document is *sealed* to prevent the situation where one map function changes document state and another receives a modified version. For efficiency reasons, documents are passed to a group of map functions - each document is processed by a group of map functions from all views of the related design document. This means that if you trigger an index update for one view in the design document, all others will get updated too. Since version `1.1.0`, `map` supports :ref:`CommonJS ` modules and the :func:`require` function. .. _reducefun: Reduce and Rereduce Functions ----------------------------- .. function:: redfun(keys, values[, rereduce]) :param keys: Array of pairs of key-docid for related map function results. Always ``null`` if rereduce is running (has ``true`` value). :param values: Array of map function result values. :param rereduce: Boolean flag to indicate a rereduce run. :return: Reduces `values` Reduce functions take two required arguments of keys and values lists - the result of the related map function - and an optional third value which indicates if `rereduce` mode is active or not. `Rereduce` is used for additional reduce values list, so when it is ``true`` there is no information about related `keys` (first argument is ``null``). Note that if the result of a `reduce` function is longer than the initial values list then a Query Server error will be raised. However, this behavior can be disabled by setting ``reduce_limit`` config option to ``false``: .. code-block:: ini [query_server_config] reduce_limit = false While disabling ``reduce_limit`` might be useful for debug proposes, remember that the main task of reduce functions is to *reduce* the mapped result, not to make it bigger. Generally, your reduce function should converge rapidly to a single value - which could be an array or similar object. .. _reducefun/builtin: Built-in Reduce Functions ^^^^^^^^^^^^^^^^^^^^^^^^^ Additionally, CouchDB has a set of built-in reduce functions. These are implemented in Erlang and run inside CouchDB, so they are much faster than the equivalent JavaScript functions. .. data:: _approx_count_distinct .. versionadded:: 2.2 Approximates the number of distinct keys in a view index using a variant of the `HyperLogLog`_ algorithm. This algorithm enables an efficient, parallelizable computation of cardinality using fixed memory resources. CouchDB has configured the underlying data structure to have a relative error of ~2%. .. _HyperLogLog: https://en.wikipedia.org/wiki/HyperLogLog As this reducer ignores the emitted values entirely, an invocation with ``group=true`` will simply return a value of 1 for every distinct key in the view. In the case of array keys, querying the view with a ``group_level`` specified will return the number of distinct keys that share the common group prefix in each row. The algorithm is also cognizant of the ``startkey`` and ``endkey`` boundaries and will return the number of distinct keys within the specified key range. A final note regarding Unicode collation: this reduce function uses the binary representation of each key in the index directly as input to the HyperLogLog filter. As such, it will (incorrectly) consider keys that are not byte identical but that compare equal according to the Unicode collation rules to be distinct keys, and thus has the potential to overestimate the cardinality of the key space if a large number of such keys exist. .. data:: _count Counts the number of values in the index with a given key. This could be implemented in JavaScript as: .. code-block:: javascript // could be replaced by _count function(keys, values, rereduce) { if (rereduce) { return sum(values); } else { return values.length; } } .. data:: _stats Computes the following quantities for numeric values associated with each key: ``sum``, ``min``, ``max``, ``count``, and ``sumsqr``. The behavior of the ``_stats`` function varies depending on the output of the map function. The simplest case is when the map phase emits a single numeric value for each key. In this case the ``_stats`` function is equivalent to the following JavaScript: .. code-block:: javascript // could be replaced by _stats function(keys, values, rereduce) { if (rereduce) { return { 'sum': values.reduce(function(a, b) { return a + b.sum }, 0), 'min': values.reduce(function(a, b) { return Math.min(a, b.min) }, Infinity), 'max': values.reduce(function(a, b) { return Math.max(a, b.max) }, -Infinity), 'count': values.reduce(function(a, b) { return a + b.count }, 0), 'sumsqr': values.reduce(function(a, b) { return a + b.sumsqr }, 0) } } else { return { 'sum': sum(values), 'min': Math.min.apply(null, values), 'max': Math.max.apply(null, values), 'count': values.length, 'sumsqr': (function() { var sumsqr = 0; values.forEach(function (value) { sumsqr += value * value; }); return sumsqr; })(), } } } The ``_stats`` function will also work with "pre-aggregated" values from a map phase. A map function that emits an object containing ``sum``, ``min``, ``max``, ``count``, and ``sumsqr`` keys and numeric values for each can use the ``_stats`` function to combine these results with the data from other documents. The emitted object may contain other keys (these are ignored by the reducer), and it is also possible to mix raw numeric values and pre-aggregated objects in a single view and obtain the correct aggregated statistics. Finally, ``_stats`` can operate on key-value pairs where each value is an array comprised of numbers or pre-aggregated objects. In this case **every** value emitted from the map function must be an array, and the arrays must all be the same length, as ``_stats`` will compute the statistical quantities above *independently* for each element in the array. Users who want to compute statistics on multiple values from a single document should either ``emit`` each value into the index separately, or compute the statistics for the set of values using the JavaScript example above and emit a pre-aggregated object. .. data:: _sum In its simplest variation, ``_sum`` sums the numeric values associated with each key, as in the following JavaScript: .. code-block:: javascript // could be replaced by _sum function(keys, values) { return sum(values); } As with ``_stats``, the ``_sum`` function offers a number of extended capabilities. The ``_sum`` function requires that map values be numbers, arrays of numbers, or objects. When presented with array output from a map function, ``_sum`` will compute the sum for every element of the array. A bare numeric value will be treated as an array with a single element, and arrays with fewer elements will be treated as if they contained zeroes for every additional element in the longest emitted array. As an example, consider the following map output: .. code-block:: javascript {"total_rows":5, "offset":0, "rows": [ {"id":"id1", "key":"abc", "value": 2}, {"id":"id2", "key":"abc", "value": [3,5,7]}, {"id":"id2", "key":"def", "value": [0,0,0,42]}, {"id":"id2", "key":"ghi", "value": 1}, {"id":"id1", "key":"ghi", "value": 3} ]} The ``_sum`` for this output without any grouping would be: .. code-block:: javascript {"rows": [ {"key":null, "value": [9,5,7,42]} ]} while the grouped output would be .. code-block:: javascript {"rows": [ {"key":"abc", "value": [5,5,7]}, {"key":"def", "value": [0,0,0,42]}, {"key":"ghi", "value": 4 ]} This is in contrast to the behavior of the ``_stats`` function which requires that all emitted values be arrays of identical length if any array is emitted. It is also possible to have ``_sum`` recursively descend through an emitted object and compute the sums for every field in the object. Objects *cannot* be mixed with other data structures. Objects can be arbitrarily nested, provided that the values for all fields are themselves numbers, arrays of numbers, or objects. .. note:: **Why don't reduce functions support CommonJS modules?** While `map` functions have limited access to stored modules through :func:`require`, there is no such feature for `reduce` functions. The reason lies deep inside the way `map` and `reduce` functions are processed by the Query Server. Let's take a look at `map` functions first: #. CouchDB sends all `map` functions in a processed design document to the Query Server. #. the Query Server handles them one by one, compiles and puts them onto an internal stack. #. after all `map` functions have been processed, CouchDB will send the remaining documents for indexing, one by one. #. the Query Server receives the document object and applies it to every function from the stack. The emitted results are then joined into a single array and sent back to CouchDB. Now let's see how `reduce` functions are handled: #. CouchDB sends *as a single command* the list of available `reduce` functions with the result list of key-value pairs that were previously returned from the `map` functions. #. the Query Server compiles the reduce functions and applies them to the key-value lists. The reduced result is sent back to CouchDB. As you may note, `reduce` functions are applied in a single shot to the map results while `map` functions are applied to documents one by one. This means that it's possible for `map` functions to precompile CommonJS libraries and use them during the entire view processing, but for `reduce` functions they would be compiled again and again for each view result reduction, which would lead to performance degradation. .. _showfun: Show Functions ============== .. warning:: Show functions are deprecated in CouchDB 3.0, and will be removed in CouchDB 4.0. .. function:: showfun(doc, req) :param doc: The document that is being processed; may be omitted. :param req: :ref:`Request object `. :return: :ref:`Response object ` :rtype: object or string Show functions are used to represent documents in various formats, commonly as HTML pages with nice formatting. They can also be used to run server-side functions without requiring a pre-existing document. Basic example of show function could be: .. code-block:: javascript function(doc, req){ if (doc) { return "Hello from " + doc._id + "!"; } else { return "Hello, world!"; } } Also, there is more simple way to return json encoded data: .. code-block:: javascript function(doc, req){ return { 'json': { 'id': doc['_id'], 'rev': doc['_rev'] } } } and even files (this one is CouchDB logo): .. code-block:: javascript function(doc, req){ return { 'headers': { 'Content-Type' : 'image/png', }, 'base64': ''.concat( 'iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAMAAAAoLQ9TAAAAsV', 'BMVEUAAAD////////////////////////5ur3rEBn////////////////wDBL/', 'AADuBAe9EB3IEBz/7+//X1/qBQn2AgP/f3/ilpzsDxfpChDtDhXeCA76AQH/v7', '/84eLyWV/uc3bJPEf/Dw/uw8bRWmP1h4zxSlD6YGHuQ0f6g4XyQkXvCA36MDH6', 'wMH/z8/yAwX64ODeh47BHiv/Ly/20dLQLTj98PDXWmP/Pz//39/wGyJ7Iy9JAA', 'AADHRSTlMAbw8vf08/bz+Pv19jK/W3AAAAg0lEQVR4Xp3LRQ4DQRBD0QqTm4Y5', 'zMxw/4OleiJlHeUtv2X6RbNO1Uqj9g0RMCuQO0vBIg4vMFeOpCWIWmDOw82fZx', 'vaND1c8OG4vrdOqD8YwgpDYDxRgkSm5rwu0nQVBJuMg++pLXZyr5jnc1BaH4GT', 'LvEliY253nA3pVhQqdPt0f/erJkMGMB8xucAAAAASUVORK5CYII=') } } But what if you need to represent data in different formats via a single function? Functions :func:`registerType` and :func:`provides` are your the best friends in that question: .. code-block:: javascript function(doc, req){ provides('json', function(){ return {'json': doc} }); provides('html', function(){ return '
' + toJSON(doc) + '
' }) provides('xml', function(){ return { 'headers': {'Content-Type': 'application/xml'}, 'body' : ''.concat( '\n', '', (function(){ escape = function(s){ return s.replace(/"/g, '"') .replace(/>/g, '>') .replace(/</g, '<') .replace(/&/g, '&'); }; var content = ''; for(var key in doc){ if(!doc.hasOwnProperty(key)) continue; var value = escape(toJSON(doc[key])); var key = escape(key); content += ''.concat( '<' + key + '>', value '' ) } return content; })(), '' ) } }) registerType('text-json', 'text/json') provides('text-json', function(){ return toJSON(doc); }) } This function may return `html`, `json` , `xml` or our custom `text json` format representation of same document object with same processing rules. Probably, the `xml` provider in our function needs more care to handle nested objects correctly, and keys with invalid characters, but you've got the idea! .. seealso:: CouchDB Guide: - `Show Functions `_ .. _listfun: List Functions ============== .. warning:: List functions are deprecated in CouchDB 3.0, and will be removed in CouchDB 4.0. .. function:: listfun(head, req) :param head: :ref:`view_head_info_object` :param req: :ref:`Request object `. :return: Last chunk. :rtype: string While :ref:`showfun` are used to customize document presentation, :ref:`listfun` are used for the same purpose, but on :ref:`viewfun` results. The following list function formats the view and represents it as a very simple HTML page: .. code-block:: javascript function(head, req){ start({ 'headers': { 'Content-Type': 'text/html' } }); send(''); send(''); while(row = getRow()){ send(''.concat( '', '', '', '', '' )); } send('
IDKeyValue
' + toJSON(row.id) + '' + toJSON(row.key) + '' + toJSON(row.value) + '
'); } Templates and styles could obviously be used to present data in a nicer fashion, but this is an excellent starting point. Note that you may also use :func:`registerType` and :func:`provides` functions in a similar way as for :ref:`showfun`! However, note that :func:`provides` expects the return value to be a string when used inside a list function, so you'll need to use :func:`start` to set any custom headers and stringify your JSON before returning it. .. seealso:: CouchDB Guide: - `Transforming Views with List Functions `_ .. _updatefun: Update Functions ================ .. function:: updatefun(doc, req) :param doc: The document that is being processed. :param req: :ref:`request_object` :returns: Two-element array: the first element is the (updated or new) document, which is committed to the database. If the first element is ``null`` no document will be committed to the database. If you are updating an existing document, it should already have an ``_id`` set, and if you are creating a new document, make sure to set its ``_id`` to something, either generated based on the input or the ``req.uuid`` provided. The second element is the response that will be sent back to the caller. Update handlers are functions that clients can request to invoke server-side logic that will create or update a document. This feature allows a range of use cases such as providing a server-side last modified timestamp, updating individual fields in a document without first getting the latest revision, etc. When the request to an update handler includes a document ID in the URL, the server will provide the function with the most recent version of that document. You can provide any other values needed by the update handler function via the ``POST``/``PUT`` entity body or query string parameters of the request. A basic example that demonstrates all use-cases of update handlers: .. code-block:: javascript function(doc, req){ if (!doc){ if ('id' in req && req['id']){ // create new document return [{'_id': req['id']}, 'New World'] } // change nothing in database return [null, 'Empty World'] } doc['world'] = 'hello'; doc['edited_by'] = req['userCtx']['name'] return [doc, 'Edited World!'] } .. _filterfun: Filter Functions ================ .. function:: filterfun(doc, req) :param doc: The document that is being processed :param req: :ref:`request_object` :return: Boolean value: ``true`` means that `doc` passes the filter rules, ``false`` means that it does not. Filter functions mostly act like :ref:`showfun` and :ref:`listfun`: they format, or *filter* the :ref:`changes feed`. Classic Filters --------------- By default the changes feed emits all database documents changes. But if you're waiting for some special changes, processing all documents is inefficient. Filters are special design document functions that allow the changes feed to emit only specific documents that pass filter rules. Let's assume that our database is a mailbox and we need to handle only new mail events (documents with the status `new`). Our filter function would look like this: .. code-block:: javascript function(doc, req){ // we need only `mail` documents if (doc.type != 'mail'){ return false; } // we're interested only in `new` ones if (doc.status != 'new'){ return false; } return true; // passed! } Filter functions must return ``true`` if a document passed all the rules. Now, if you apply this function to the changes feed it will emit only changes about "new mails":: GET /somedatabase/_changes?filter=mailbox/new_mail HTTP/1.1 .. code-block:: javascript {"results":[ {"seq":"1-g1AAAAF9eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBMZc4EC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HqQ_kQG3qgSQqnoCqvJYgCRDA5ACKpxPWOUCiMr9hFUegKi8T1jlA4hKkDuzAC2yZRo","id":"df8eca9da37dade42ee4d7aa3401f1dd","changes":[{"rev":"1-c2e0085a21d34fa1cecb6dc26a4ae657"}]}, {"seq":"9-g1AAAAIreJyVkEsKwjAURUMrqCOXoCuQ5MU0OrI70XyppcaRY92J7kR3ojupaSPUUgqWwAu85By4t0AITbJYo5k7aUNSAnyJ_SGFf4gEkvOyLPMsFtHRL8ZKaC1M0v3eq5ALP-X2a0G1xYKhgnONpmenjT04o_v5tOJ3LV5itTES_uP3FX9ppcAACaVsQAo38hNd_eVFt8ZklVljPqSPYLoH06PJhG0Cxq7-yhQcz-B4_fQCjFuqBjjewVF3E9cORoExSrpU_gHBTo5m","id":"df8eca9da37dade42ee4d7aa34024714","changes":[{"rev":"1-29d748a6e87b43db967fe338bcb08d74"}]}, ], "last_seq":"10-g1AAAAIreJyVkEsKwjAURR9tQR25BF2B5GMaHdmdaNIk1FLjyLHuRHeiO9Gd1LQRaimFlsALvOQcuLcAgGkWKpjbs9I4wYSvkDu4cA-BALkoyzLPQhGc3GKSCqWEjrvfexVy6abc_SxQWwzRVHCuYHaxSpuj1aqfTyp-3-IlSrdakmH8oeKvrRSIkJhSNiKFjdyEm7uc6N6YTKo3iI_pw5se3vRsMiETE23WgzJ5x8s73n-9EMYNTUc4Pt5RdxPVDkYJYxR3qfwLwW6OZw"} Note that the value of ``last_seq`` is `10-..`, but we received only two records. Seems like any other changes were for documents that haven't passed our filter. We probably need to filter the changes feed of our mailbox by more than a single status value. We're also interested in statuses like "spam" to update spam-filter heuristic rules, "outgoing" to let a mail daemon actually send mails, and so on. Creating a lot of similar functions that actually do similar work isn't good idea - so we need a dynamic filter. You may have noticed that filter functions take a second argument named :ref:`request `. This allows the creation of dynamic filters based on query parameters, :ref:`user context ` and more. The dynamic version of our filter looks like this: .. code-block:: javascript function(doc, req){ // we need only `mail` documents if (doc.type != 'mail'){ return false; } // we're interested only in requested status if (doc.status != req.query.status){ return false; } return true; // passed! } and now we have passed the `status` query parameter in the request to let our filter match only the required documents:: GET /somedatabase/_changes?filter=mailbox/by_status&status=new HTTP/1.1 .. code-block:: javascript {"results":[ {"seq":"1-g1AAAAF9eJzLYWBg4MhgTmHgz8tPSTV0MDQy1zMAQsMcoARTIkOS_P___7MymBMZc4EC7MmJKSmJqWaYynEakaQAJJPsoaYwgE1JM0o1TjQ3T2HgLM1LSU3LzEtNwa3fAaQ_HqQ_kQG3qgSQqnoCqvJYgCRDA5ACKpxPWOUCiMr9hFUegKi8T1jlA4hKkDuzAC2yZRo","id":"df8eca9da37dade42ee4d7aa3401f1dd","changes":[{"rev":"1-c2e0085a21d34fa1cecb6dc26a4ae657"}]}, {"seq":"9-g1AAAAIreJyVkEsKwjAURUMrqCOXoCuQ5MU0OrI70XyppcaRY92J7kR3ojupaSPUUgqWwAu85By4t0AITbJYo5k7aUNSAnyJ_SGFf4gEkvOyLPMsFtHRL8ZKaC1M0v3eq5ALP-X2a0G1xYKhgnONpmenjT04o_v5tOJ3LV5itTES_uP3FX9ppcAACaVsQAo38hNd_eVFt8ZklVljPqSPYLoH06PJhG0Cxq7-yhQcz-B4_fQCjFuqBjjewVF3E9cORoExSrpU_gHBTo5m","id":"df8eca9da37dade42ee4d7aa34024714","changes":[{"rev":"1-29d748a6e87b43db967fe338bcb08d74"}]}, ], "last_seq":"10-g1AAAAIreJyVkEsKwjAURR9tQR25BF2B5GMaHdmdaNIk1FLjyLHuRHeiO9Gd1LQRaimFlsALvOQcuLcAgGkWKpjbs9I4wYSvkDu4cA-BALkoyzLPQhGc3GKSCqWEjrvfexVy6abc_SxQWwzRVHCuYHaxSpuj1aqfTyp-3-IlSrdakmH8oeKvrRSIkJhSNiKFjdyEm7uc6N6YTKo3iI_pw5se3vRsMiETE23WgzJ5x8s73n-9EMYNTUc4Pt5RdxPVDkYJYxR3qfwLwW6OZw"} and we can easily change filter behavior with:: GET /somedatabase/_changes?filter=mailbox/by_status&status=spam HTTP/1.1 .. code-block:: javascript {"results":[ {"seq":"6-g1AAAAIreJyVkM0JwjAYQD9bQT05gk4gaWIaPdlNNL_UUuPJs26im-gmuklMjVClFFoCXyDJe_BSAsA4jxVM7VHpJEswWyC_ktJfRBzEzDlX5DGPDv5gJLlSXKfN560KMfdTbL4W-FgM1oQzpmByskqbvdWqnc8qfvvHCyTXWuBu_K7iz38VCOOUENqjwg79hIvfvOhamQahROoVYn3-I5huwXSvm5BJsTbLTk3B8QiO58-_YMoMkT0cr-BwdRElmFKSNKniDcAcjmM","id":"8960e91220798fc9f9d29d24ed612e0d","changes":[{"rev":"3-cc6ff71af716ddc2ba114967025c0ee0"}]}, ], "last_seq":"10-g1AAAAIreJyVkEsKwjAURR9tQR25BF2B5GMaHdmdaNIk1FLjyLHuRHeiO9Gd1LQRaimFlsALvOQcuLcAgGkWKpjbs9I4wYSvkDu4cA-BALkoyzLPQhGc3GKSCqWEjrvfexVy6abc_SxQWwzRVHCuYHaxSpuj1aqfTyp-3-IlSrdakmH8oeKvrRSIkJhSNiKFjdyEm7uc6N6YTKo3iI_pw5se3vRsMiETE23WgzJ5x8s73n-9EMYNTUc4Pt5RdxPVDkYJYxR3qfwLwW6OZw"} Combining filters with a `continuous` feed allows creating powerful event-driven systems. .. _viewfilter: View Filters ------------ View filters are the same as classic filters above, with one small difference: they use the `map` instead of the `filter` function of a view, to filter the changes feed. Each time a key-value pair is emitted from the `map` function, a change is returned. This allows avoiding filter functions that mostly do the same work as views. To use them just pass `filter=_view` and `view=designdoc/viewname` as request parameters to the :ref:`changes feed`:: GET /somedatabase/_changes?filter=_view&view=dname/viewname HTTP/1.1 .. note:: Since view filters use `map` functions as filters, they can't show any dynamic behavior since :ref:`request object` is not available. .. seealso:: CouchDB Guide: - `Guide to filter change notification `_ .. _vdufun: Validate Document Update Functions ================================== .. function:: validatefun(newDoc, oldDoc, userCtx, secObj) :param newDoc: New version of document that will be stored. :param oldDoc: Previous version of document that is already stored. :param userCtx: :ref:`userctx_object` :param secObj: :ref:`security_object` :throws: ``forbidden`` error to gracefully prevent document storing. :throws: ``unauthorized`` error to prevent storage and allow the user to re-auth. A design document may contain a function named `validate_doc_update` which can be used to prevent invalid or unauthorized document update requests from being stored. The function is passed the new document from the update request, the current document stored in the database, a :ref:`userctx_object` containing information about the user writing the document (if present), and a :ref:`security_object` with lists of database security roles. Validation functions typically examine the structure of the new document to ensure that required fields are present and to verify that the requesting user should be allowed to make changes to the document properties. For example, an application may require that a user must be authenticated in order to create a new document or that specific document fields be present when a document is updated. The validation function can abort the pending document write by throwing one of two error objects: .. code-block:: javascript // user is not authorized to make the change but may re-authenticate throw({ unauthorized: 'Error message here.' }); // change is not allowed throw({ forbidden: 'Error message here.' }); Document validation is optional, and each design document in the database may have at most one validation function. When a write request is received for a given database, the validation function in each design document in that database is called in an unspecified order. If any of the validation functions throw an error, the write will not succeed. **Example**: The ``_design/_auth`` ddoc from `_users` database uses a validation function to ensure that documents contain some required fields and are only modified by a user with the ``_admin`` role: .. code-block:: javascript function(newDoc, oldDoc, userCtx, secObj) { if (newDoc._deleted === true) { // allow deletes by admins and matching users // without checking the other fields if ((userCtx.roles.indexOf('_admin') !== -1) || (userCtx.name == oldDoc.name)) { return; } else { throw({forbidden: 'Only admins may delete other user docs.'}); } } if ((oldDoc && oldDoc.type !== 'user') || newDoc.type !== 'user') { throw({forbidden : 'doc.type must be user'}); } // we only allow user docs for now if (!newDoc.name) { throw({forbidden: 'doc.name is required'}); } if (!newDoc.roles) { throw({forbidden: 'doc.roles must exist'}); } if (!isArray(newDoc.roles)) { throw({forbidden: 'doc.roles must be an array'}); } if (newDoc._id !== ('org.couchdb.user:' + newDoc.name)) { throw({ forbidden: 'Doc ID must be of the form org.couchdb.user:name' }); } if (oldDoc) { // validate all updates if (oldDoc.name !== newDoc.name) { throw({forbidden: 'Usernames can not be changed.'}); } } if (newDoc.password_sha && !newDoc.salt) { throw({ forbidden: 'Users with password_sha must have a salt.' + 'See /_utils/script/couch.js for example code.' }); } var is_server_or_database_admin = function(userCtx, secObj) { // see if the user is a server admin if(userCtx.roles.indexOf('_admin') !== -1) { return true; // a server admin } // see if the user a database admin specified by name if(secObj && secObj.admins && secObj.admins.names) { if(secObj.admins.names.indexOf(userCtx.name) !== -1) { return true; // database admin } } // see if the user a database admin specified by role if(secObj && secObj.admins && secObj.admins.roles) { var db_roles = secObj.admins.roles; for(var idx = 0; idx < userCtx.roles.length; idx++) { var user_role = userCtx.roles[idx]; if(db_roles.indexOf(user_role) !== -1) { return true; // role matches! } } } return false; // default to no admin } if (!is_server_or_database_admin(userCtx, secObj)) { if (oldDoc) { // validate non-admin updates if (userCtx.name !== newDoc.name) { throw({ forbidden: 'You may only update your own user document.' }); } // validate role updates var oldRoles = oldDoc.roles.sort(); var newRoles = newDoc.roles.sort(); if (oldRoles.length !== newRoles.length) { throw({forbidden: 'Only _admin may edit roles'}); } for (var i = 0; i < oldRoles.length; i++) { if (oldRoles[i] !== newRoles[i]) { throw({forbidden: 'Only _admin may edit roles'}); } } } else if (newDoc.roles.length > 0) { throw({forbidden: 'Only _admin may set roles'}); } } // no system roles in users db for (var i = 0; i < newDoc.roles.length; i++) { if (newDoc.roles[i][0] === '_') { throw({ forbidden: 'No system roles (starting with underscore) in users db.' }); } } // no system names as names if (newDoc.name[0] === '_') { throw({forbidden: 'Username may not start with underscore.'}); } var badUserNameChars = [':']; for (var i = 0; i < badUserNameChars.length; i++) { if (newDoc.name.indexOf(badUserNameChars[i]) >= 0) { throw({forbidden: 'Character `' + badUserNameChars[i] + '` is not allowed in usernames.'}); } } } .. note:: The ``return`` statement is used only for function, it has no impact on the validation process. .. seealso:: CouchDB Guide: - `Validation Functions `_