suppose my data is
db.posts.save({postid:1,postdata:"hi am ",comments:["nice","whats bro"]});
so in this case how to iterate comments
means
cursor=selct * from posts;
cursor 1=selct * from comments where postid=:cursor.postid
for (i in cursor)
for(j in cursor1)
One way to iterate over the comments would be as follows:
db.posts.find().forEach(
function(doc) {
// iterate over the comments in your preferred javascript way
var i;
for (i=0; i<doc.comments.length; ++i) {
// Do whatever you want with doc.comments[i] here
}
}
)
Related
I'm using Swig as a template engine for Express.js and I found no way to make a for loop with a variable like so:
for(var i=0; i<100; i++){
//whatever
}
Is this even possible?
As posted on your github issue for the same question, loops like this don't exist in Swig. You can iterate over actual objects and arrays, however. (See for-tag documentation).
Otherwise, you could create a range helper, as discussed here
swig.setDefaults({ locals: {
range: function (start, len) {
return (new Array(len)).join().split(',').map(function (n, idx) { return idx + start; });
}
}});
i am having data in mongodb like that
[
{
"name":"silvester",
"product":"laptop,iphone,mobile,phone"
},
{
"name":"john",
"product":"cycle,bus,phone,laptop"
},
{
"name":"franklin",
"product":"cycle,phone"
}
]
How to find that laptop is in product key.
if product key look like this
{
"name":"XXX",
"product":"laptop"
}
I can easily find that name by using this db.collection.find("product":"laptop");
So how to find this?
Also let me know this three website name running under using backbone.js and node.js and mongodb technology such as www.trello.com .
sorry for my worst english..
Using regex with mongodb
This worked for me
db.collection.find({"product": /laptop/})
Updated Answer
If you wish to use variables, try something like this:
var abc = "laptop";
// other stuff
userdetails.find({"product":new RegExp(abc)}).toArray(function(err,result){
if (err) console.log ("error: "+err);
else
{
// if you want the length
console.log(result.length);
// if you actually want to see the results
for (var i = 0; i < result.length; i++)
{
console.log(result[i]);
}
}
});
Updated One More Time
var abc = "laptop";
// other stuff
// note this is case sensitive. if abc = "Laptop", it will not find it
// to make it case insensitive, you'll need to edit the RegExp constructor
// to this: new RegExp("^"+abc+",|, "+abc+"(?!\w)", "i")
userdetails.find({"product":new RegExp("^"+abc+",|, "+abc+"(?!\w)")}).toArray(function(err,result){
if (err) console.log ("error: "+err);
else
{
// if you want the length
console.log(result.length);
// if you actually want to see the results
for (var i = 0; i < result.length; i++)
{
console.log(result[i]);
}
}
});
regex will work perfectly fine. there is also good news for you as monogdb will be releasing full text search index in the upcoming version
http://docs.mongodb.org/manual/release-notes/2.4/#text-indexes
I've been playing around with Couchbase Server and now just tried replicating my local db to Cloudant, but am getting conflicting results for my map/reduce function pair to build a set of unique tags with their associated projects...
// map.js
function(doc) {
if (doc.tags) {
for(var t in doc.tags) {
emit(doc.tags[t], doc._id);
}
}
}
// reduce.js
function(key,values,rereduce) {
if (!rereduce) {
var res=[];
for(var v in values) {
res.push(values[v]);
}
return res;
} else {
return values.length;
}
}
In Cloudbase server this returns JSON like:
{"rows":[
{"key":"3d","value":["project1","project3","project8","project10"]},
{"key":"agents","value":["project2"]},
{"key":"fabrication","value":["project3","project5"]}
]}
That's exactly what I wanted & expected. However, the same query on the Cloudant replica, returns this:
{"rows":[
{"key":"3d","value":4},
{"key":"agents","value":1},
{"key":"fabrication","value":2}
]}
So it somehow only returns the length of the value array... Highly confusing & am grateful for any insights by some M&R ninjas... ;)
It looks like this is exactly the behavior you would expect given your reduce function. The key part is this:
else {
return values.length;
}
In Cloudant, rereduce is always called (since the reduce needs to span over multiple shards.) In this case, rereduce calls values.length, which will only return the length of the array.
I prefer to reduce/re-reduce implicitly rather than depending on the rereduce parameter.
function(doc) { // map
if (doc.tags) {
for(var t in doc.tags) {
emit(doc.tags[t], {id:doc._id, tag:doc.tags[t]});
}
}
}
Then reduce checks whether it is accumulating document ids from the identical tag, or whether it is just counting different tags.
function(keys, vals, rereduce) {
var initial_tag = vals[0].tag;
return vals.reduce(function(state, val) {
if(initial_tag && val.tag === initial_tag) {
// Accumulate ids which produced this tag.
var ids = state.ids;
if(!ids)
ids = [ state.id ]; // Build initial list from the state's id.
return { tag: val.tag,
, ids: ids.concat([val.id])
};
} else {
var state_count = state.ids ? state.ids.length : state;
var val_count = val.ids ? val.ids.length : val;
return state_count + val_count;
}
})
}
(I didn't test this code, but you get the idea. As long as the tag value is the same, it doesn't matter whether it's a reduce or rereduce. Once different tags start reducing together, it detects that because the tag value will change. So at that point just start accumulating.
I have used this trick before, although IMO it's rarely worth it.
Also in your specific case, this is a dangerous reduce function. You are building a wide list to see all the docs that have a tag. CouchDB likes tall lists, not fat lists. If you want to see all the docs that have a tag, you could map them.
for(var a = 0; a < doc.tags.length; a++) {
emit(doc.tags[a], doc._id);
}
Now you can query /db/_design/app/_view/docs_by_tag?key="3d" and you should get
{"total_rows":287,"offset":30,"rows":[
{"id":"project1","key":"3d","value":"project1"}
{"id":"project3","key":"3d","value":"project3"}
{"id":"project8","key":"3d","value":"project8"}
{"id":"project10","key":"3d","value":"project10"}
]}
Let's say I have blog entries like these in my CouchDB database:
{"name":"Mary", "postdate":"20110412", "subject":"this", "message":"blah"}
{"name":"Joe", "postdate":"20110411", "subject":"that", "message":"yadda"}
{"name":"Mary", "postdate":"20110411", "subject":"and this", "message":"blah-blah"}
{"name":"Joe", "postdate":"20110410", "subject":"And other thing", "message":"yada-yada"}
{"name":"Jane", "postdate":"20110409", "subject":"Serious stuff", "message":"Not really"}
It's pretty easy to get a list of all posts. But how do I get a list of latest posts from all the users?
Like that:
{"name":"Mary", "postdate":"20110412", "subject":"this", "message":"blah"}
{"name":"Joe", "postdate":"20110411", "subject":"that", "message":"yadda"}
{"name":"Jane", "postdate":"20110409", "subject":"Serious stuff", "message":"Not really"}
Try with this map function:
function(doc) {
if (doc.postdate && doc.name) {
emit([doc.name, doc.postdate], 1);
}
}
and the following reduce function:
function(keys, values, rereduce) {
var max = 0,
ks = rereduce ? values : keys;
for (var i = 1, l = ks.length; i < l; ++i) {
if (ks[max][0][1] < ks[i][0][1]) max = i;
}
return ks[max];
}
and query it with group_level=1. It gives you the _id of the posts, then you can retrieve them all with a single query with the keys parameter or using a POST.
I am not sure if this is the best approach, but it seems to work.
UPDATE: fixed map to handle rereduce correctly.
You're going to emit the postdate as the key because keys are sorted. For example, this is what your map function will look like...
function(doc) {
if(doc.postdate) {
emit(doc.postdate, doc);
}
}
That will give you all the docs sorted ascending by postdate. If you want descending then query with ?descending=true
Cheers.
How would I execute a query equivalent to "select top 10" in couch db?
For example I have a "schema" like so:
title body modified
and I want to select the last 10 modified documents.
As an added bonus if anyone can come up with a way to do the same only per category. So for:
title category body modified
return a list of latest 10 documents in each category.
I am just wondering if such a query is possible in couchdb.
To get the first 10 documents from your db you can use the limit query option.
E.g. calling
http://localhost:5984/yourdb/_design/design_doc/_view/view_name?limit=10
You get the first 10 documents.
View rows are sorted by the key; adding descending=true in the querystring will reverse their order. You can also emit only the documents you are interested using again the querystring to select the keys you are interested.
So in your view you write your map function like:
function(doc) {
emit([doc.category, doc.modified], doc);
}
And you query it like this:
http://localhost:5984/yourdb/_design/design_doc/_view/view_name?startkey=["youcategory"]&endkey=["youcategory", date_in_the_future]&limit=10&descending=true
here is what you need to do.
Map function
function(doc)
{
if (doc.category)
{
emit(['category', doc.category], doc.modified);
}
}
then you need a list function that groups them, you might be temped to abuse a reduce and do this, but it will probably throw errors because of not reducing fast enough with large sets of data.
function(head, req)
{
% this sort function assumes that modifed is a number
% and it sorts in descending order
function sortCategory(a,b) { b.value - a.value; }
var categories = {};
var category;
var id;
var row;
while (row = getRow())
{
if (!categories[row.key[0]])
{
categories[row.key[0]] = [];
}
categories[row.key[0]].push(row);
}
for (var cat in categories)
{
categories[cat].sort(sortCategory);
categories[cat] = categories[cat].slice(0,10);
}
send(toJSON(categories));
}
you can get all categories top 10 now with
http://localhost:5984/database/_design/doc/_list/top_ten/by_categories
and get the docs with
http://localhost:5984/database/_design/doc/_list/top_ten/by_categories?include_docs=true
now you can query this with a multiple range POST and limit which categories
curl -X POST http://localhost:5984/database/_design/doc/_list/top_ten/by_categories -d '{"keys":[["category1"],["category2",["category3"]]}'
you could also not hard code the 10 and pass the number in through the req variable.
Here is some more View/List trickery.
slight correction. it was not sorting untill I added the "return" keyword in your sortCategory function. It should be like this:
function sortCategory(a,b) { return b.value - a.value; }