Is it possible to use similiar query in CouchDB? Like use two keys?
SELECT field FROM table WHERE value1="key1" OR value2="key2"
I was always using only one key.
function(doc) {
emit(doc.title, doc);
}
Thank you.
In CouchDB 0.9 and above you can POST to a view (or _all_docs) with a body like:
{"keys": ["key1", "key2", ...]}
In order to retrieve the set of rows with the matching keys.
Yes. Something like this should do the trick if I understand your question:
function(doc) {
a = (doc.value1 && doc.value1 == "key1");
b = (doc.value2 && doc.value2 == "key2");
if (a || b) {
emit(doc._id,doc.title);
}
}
Only emit the documents or values you need.
I'd add this to duluthian's reply:
emit(doc.title, null)
You can always pull out the "_id" and doc values using the view api.
You could create a view like this:
function(doc){
if(doc.value1) emit(doc.value1, doc.field);
if(doc.value2) emit(doc.value2, doc.field);
}
Then query it using llasram's suggestion to POST to the view with:
{"keys": ["key1", "key2", ...]}
Your client will have to be wary of dups though. A document where doc.value1 == "key1" && doc.value2 == "key2" will show up twice. Just use _id to filter the results.
One needs to expand a little bit on llasram's answer; the index must contain the values for both fields:
function(doc) {
emit("value1:"+doc.value1); // add check for undefined, null, etc.
emit("value2:"+doc.value2);
}
then query with
keys=["value1:key1","value2:key2"]
EDIT: This will however report the same document multiple times if it contains the matching value+key pairs.
You could do this ( assuming you want "dynamic parameters" ) by using 2 separate views, and a little client-side processing:
You would have one view on "field1", which you would query with "value1".
( getting a list of document IDs )
Then you query a second view on "field2", passing "value2", and getting another list of Doc IDs.
Now, you simply have to find the "intersection" of the 2 lists of ID numbers
( left as an exercise for the reader )
Related
I have posts that have fields like username (author of the post) and timestamp (uploaded time). I am struggling to create a view, which when queried on, grabs posts by a particular user in descending order of the timestamp.
map: function(doc) {
if (doc.type == 'post'){
emit(doc.username, [doc._id, doc.timestamp]);
};
},
I can query documents authored by a particular user but how do I apply descending = true only on the timestamp field?
With CouchDB views, only the key can determine the sort order for the index. The value does not factor into sorting/grouping at all.
Thus, if you want to have a view that outputs posts by a user in order of creation (ascending or descending), you'll emit an array as a sort of "composite key". I would highly recommend reading through the Guide to Views in the CouchDB documentation.
For your example, I would make a map function like this:
function (doc) {
if (doc.type === 'post') {
emit([ doc.username, doc.timestamp ]);
}
}
Then, you can get the posts for a specific user with a query like:
?start_key=["username"]&end_key=["username","\ufff0"]
Which will find the posts for the given "username" ordered by the timestamp ascending. To reverse the ordering, use the following query instead:
?start_key=["username","\ufff0"]&end_key=["username"]&descending=true
Note that the values for start_key and end_key have swapped, and descending=true has been added.
As mentioned before, read through their documentation as it's an excellent way to wrap your head around the best way to use CouchDB views.
I'm brand new to CouchDB (and NoSQL in general), and am creating a simple Node.js + express + nano app to get a feel for it. It's a simple collection of books with two fields, 'title' and 'author'.
Example document:
{
"_id": "1223e03eade70ae11c9a3a20790001a9",
"_rev": "2-2e54b7aa874059a9180ac357c2c78e99",
"title": "The Art of War",
"author": "Sun Tzu"
}
Reduce function:
function(doc) {
if (doc.title && doc.author) {
emit(doc.title, doc.author);
}
}
Since CouchDB sorts by key and supports a 'descending=true' query param, it was easy to implement a filter in the UI to toggle sort order on the title, which is the key in my results set. Here's the UI:
List of books with link to sort title by ascending or descending
But I'm at a complete loss on how to do this for the author field.
I've seen this question, which helped a poster sort by a numeric reduce value, and I've read a blog post that uses a list to also sort by a reduce value, but I've not seen any way to do this on a string value without a reduce.
If you want to sort by a particular property, you need to ensure that that property is the key (or, in the case of an array key, the first element in the array).
I would recommend using the sort key as the key, emitting a null value and using include_docs to fetch the full document to allow you to display multiple properties in the UI (this also keeps the deserialized value consistent so you don't need to change how you handle the return value based on sort order).
Your map functions would be as simple as the following.
For sorting by author:
function(doc) {
if (doc.title && doc.author) {
emit(doc.author, null);
}
}
For sorting by title:
function(doc) {
if (doc.title && doc.author) {
emit(doc.title, null);
}
}
Now you just need to change which view you call based on the selected sort order and ensure you use the include_docs=true parameter on your query.
You could also use a single view for this by emitting both at once...
emit(["by_author", doc.author], null);
emit(["by_title", doc.title], null);
... and then using the composite key for your query.
Using couchdb, with the following json:
{"total_rows":3,"offset":0,"rows":[ {"id":"bc26e5eae7f8c8c3486818e7e7971df0","key":{"user":"lili#abc.com","pal":["igol ≠ eagle"],"fecha":"10/5/2014"},"value":null},{"id":"cf0dc2e2874776958c59f2f544b5a750","key":{"user":"lili#abc.com","pal":["kat ≠cat"],"fecha":"10/6/2014"},"value":null},{"id":"df4ec96088ed52096db064f2ebd2310b","key":{"user":"dum#ghi.com","pal":["dok ≠ duck"],"fecha":"10/7/2014"},"value":null}]}
I would like to query for specific user AND specific date:
for example:
?user="lili#def.com"&fecha:"10/6/2014"
I also tried:
?user%3Dlili%40def.com%26fecha%3A10%2F6%2F2014
Needless to say, it isn't currently working as I expected (all results are shown, not only the register needed).
my view func is:
function(doc) {
if (doc.USER){
emit({user:doc.USER, pal:doc.palabras, fecha:doc.fecha});
}
}
Regards.
Remember that CouchDB views are simply key/value lookups that are built at index-time, not query time. At the minute you are emitting a key with no value. If you want to look something up by two values, you'll need to emit a composite key (an array):
function(doc) {
if (doc.USER) {
emit([doc.USER, doc.fecha], doc);
}
}
Then you can look up matching documents by passing the array as the key:
?key=%5B%22lili%40def.com%22%2C%20%2210%2F6%2F2014%22%5D
There are optimisations you can make to this (e.g. emitting a null value and using include_docs to reduce the size of the view) but this should set you off on the right track.
I do the same thing as Ant P but I tend to use strings.
function ( doc ) {
if ( doc.USER ) {
emit( 'user-' + doc.USER + '-' + doc.fecha, doc );
}
}
I would also highly recommend emitting null instead of doc as a value.
Remember, you can always emit more than once depending on what kind of queries you need.
For example, if you're looking for all posts by a specific user between two dates, you could do the following view.
function ( doc ) {
if ( doc.type == "post" ) {
emit( 'user-' + doc.nombre, null );
emit( 'fecha-' + doc.fecha, null );
}
}
Then you would query the view twice _view/posts?key="user-miUsario", and _view/posts?start_key="fecha-1413040000000"&end_key="fecha-1413049452904". Then, once you have all of the ids from both views, you take the intersection and use _all_docs to get your original documents.
You end up making three requests but it saves disk space in the view, the payloads are smaller because you return null, and your code is simpler because you can query the same view multiple ways.
I Want to query CouchDB and I have a specific need : my query should return the name field of documents corresponding to this condition : the id is equal or contained in a document filed (a list).
For example, the field output is the following :
"output": [
"doc_s100",
"doc_s101",
"doc_s102",
"doc_s103",
],
I want to get all the documents having in their output field "doc_s102" for example.
I wrote a view in a design document :
"backward_by_docid": {
"map": "function(doc) {if(doc.output) emit(doc.output, doc.name)}"
}
but this view works only when I have a unique value in the output field.
How can I resolve this query ?
Thanks !
you have to iterate over the array:
if(doc.output) {
for (var curOutput in doc.output) {
emit (doc.output[curOutput],doc.name);
}
}
make sure that output always is an array (at least [])
.. and, of course use key="xx" instead key=["xxx"]
I would like to use CouchDB to store some data for me and then use RESTful api calls to get the data that I need. My database is called "test" and my documents all have a similar structure and look something like this (where hello_world is the document ID):
"hello_world" : {"id":123, "tags":["hello", "world"], "text":"Hello World"}
"foo_bar" :{"id":124, "tags":["foo", "bar"], "text":"Foo Bar"}
What I'd like to be able to do is have my users send a query such as: "Give me all the documents that contain the words 'hello world', for example. I've been playing around with views but it looks like they will only allow me to move one or more of those values into the "key" portion of the map function. That gives me the ability to do something like this:
http://localhost:5984/test/_design/search/_view/search_view?key="hello"
But this doesn't allow me to let my users specify their query string. For example, what if they searched for "hello world". I'd have to do two queries: one for "hello" and one for "world" then I'd have to write a bunch of javascript to combine the results, remove duplicates, etc (YUCK!). What I really want is to be able to do something like this:
http://localhost:5984/test/_design/search/_view/search_view?term="hello world"
Then use the parameter "hello world" in the views map/reduce functions to find all the documents that contain both "hello" and "world" in the tags array. Is this sort of thing even possible with CouchDB? Is there another way to accomplish this inside a view that I'm not thinking of?
CouchDB Views do not support facetted search or fulltext search or result intersection. The couchdb-lucene plugin lets you do all these things.
http://github.com/rnewson/couchdb-lucene/tree/master
Technically this is possible if you emit for each document each set of the powerset of the tags of the document as the key. The key set element must be ordered and your query whould have to query the tags ordered, too.
function map(doc) {
function powerset(array) { ... }
powerset_of_tags = powerset(doc.tags)
for(i in powerset_of_tags) {
emit(powerset_of_tags[i], doc);
}
}
for the doc {"hello_world" : {"id":123, "tags":["hello", "world"], "text":"Hello World"} this would emit:
{ key: [], doc: ... }
{ key: ['hello'], doc: ... }
{ key: ['world'], doc: ... }
{ key: ['hello', 'world'], doc: ... }
Although is this possible I would consider this a rather arkward solution. I don't want to imagine the disk usage of the view for a larger number of tags. I expect the number of emitted keys to grow like 2^n.
under the hood, couchdb stores data by b-tree thus you should use views to pre-process, the limitation in this case that is you can not search regex. The alternative, you can search by prefixes or suffixes from the key in views.
Note: don't use emit(key, doc), it will clone document, you should use emit(key, null) or emit(key) and add "include_docs = true" when query.
You can use yours tags as key to query.
//view function
function (doc) {
if (doc.type === "hello") {
emit(doc);
}
}
//mango query
db
.query(your_view_name,
{ startkey: startkey, endkey: endkey, include_docs: true });
Note:
endkey = startkey + "\uffff";
startkey = "h", "he", "hell"...
Plus: don't never use mango query to query regex if you don't want performance go to the hell, sences. I fixed performance issue from 2 minutes to 2 seconds by view function.