I am creating one application where for every product I have one database and I will create different document based on date. The keys in documents could be different and depend upon user, what he provides. Assumption is user will keep giving same key for tracking with changed value over time. In the end, I need to know all possible keys before creating automatic views on them.
Example:
If I had DB, say, test. It contains, say, two documents,
1. {
"_id":"1",
"_rev":"1-"
"type": "Note",
"content": "Hello World!"
}
2. {
"_id":"2",
"_rev":"1-"
"type": "Note",
"content": "Beyond Hello World!",
"extra":"Boom"
}
Then I want to list all keys in this DB. So, answer should be _id,_rev,type,content and extra.
These keys are dynamic and depend upon users. So, I couldn't assume that I knew them in advance.
I have never used stackoverflow before, I saw your question when trying to solve this problem myself so I have signed up. I think this solves your problem:
create a view where "views" includes this:
{
"keys": {
"map": "function(doc) { for (var thing in doc) { emit(thing,1); } }",
"reduce": "function(key,values) { return sum(values); }"
}
}
then query on that view with group=true e.g.:
http://localhost:5984/mydb/_design/myview/_view/keys?group=true
you should get back a list of all the keys in your database and a count of how often the occur.
does this help?
Related
I have a problem with querying CosmosDB document which contains a dictionary. This is an example document:
{
"siteAndDevices": {
"4cf0af44-6233-402a-b33a-e7e35dbbee6a": [
"f32d80d9-e93a-687e-97f5-676516649420",
"6a5eb9fa-c961-93a5-38cc-ecd74ada13ac",
"c90e9986-5aea-b552-e532-cd64a250ad10",
"7d4bfdca-547a-949b-ccb3-bbf0d6e5d727",
"fba51bfe-6a5e-7f25-e58a-7b0ced59b5d8",
"f2caac36-3590-020f-ebb7-5ccd04b4412c",
"1b446af7-ba74-3564-7237-05024c816a02",
"7ef3d931-131e-a639-10d4-f4dd5db834ca"
]
},
"id": "f9ef9fb6-4b70-7d3f-2bc8-c3d335018624"
}
I need to get all documents where provided guid is in the list, so in the dictionary value (I don't know dictionary key). I found an information somewhere here that it is not possible to iterate through keys in dictionary in CosmosDB (maybe it has changed since that time but I din't find any information in documentation), but maybe someone will have some idea. I cannot change form of the document.
I tried to do it in Linq, but I didn't get any results.
var query = _documentClient
.CreateDocumentQuery<Dto>(DocumentCollectionUri())
.Where(d => d.SiteAndDevices.Any(x => x.Value.Contains("f32d80d9-e93a-687e-97f5-676516649420")))
.AsDocumentQuery();
Not sure of the Linq query, but with SQL, you'd need something like this:
SELECT * FROM c
where array_contains(c.siteAndDevices['4cf0af44-6233-402a-b33a-e7e35dbbee6a'],"f32d80d9-e93a-687e-97f5-676516649420")
This is a strange document format though, as you've named your key with an id:
"siteAndDevices": {
"4cf0af44-6233-402a-b33a-e7e35dbbee6a": ["..."]
}
Your key is "4cf0af44-6233-402a-b33a-e7e35dbbee6a", which forces you to use a different syntax to reference it:
c.siteAndDevices['4cf0af44-6233-402a-b33a-e7e35dbbee6a']
You'd save yourself a lot of trouble refactoring this to something like:
{
"id": "dictionary1",
"siteAndDevices": {
"deviceId": "4cf0af44-6233-402a-b33a-e7e35dbbee6a",
"deviceValues": ["..."]
}
}
You can refactor further, such as using an array to contain multiple device id + value combos.
Currently I am working on a mobile app. Basically people can post their photos and the followers can like the photos like Instagram. I use mongodb as the database. Like instagram, there might be a lot of likes for a single photos. So using a document for a single "like" with index seems not reasonable because it will waste a lot of memory. However, I'd like a user add a like quickly. So my question is how to model the "like"? Basically the data model is much similar to instagram but using Mongodb.
No matter how you structure your overall document there are basically two things you need. That is basically a property for a "count" and a "list" of those who have already posted their "like" in order to ensure there are no duplicates submitted. Here's a basic structure:
{
"_id": ObjectId("54bb201aa3a0f26f885be2a3")
"photo": "imagename.png",
"likeCount": 0
"likes": []
}
Whatever the case, there is a unique "_id" for your "photo post" and whatever information you want, but then the other fields as mentioned. The "likes" property here is an array, and that is going to hold the unique "_id" values from the "user" objects in your system. So every "user" has their own unique identifier somewhere, either in local storage or OpenId or something, but a unique identifier. I'll stick with ObjectId for the example.
When someone submits a "like" to a post, you want to issue the following update statement:
db.photos.update(
{
"_id": ObjectId("54bb201aa3a0f26f885be2a3"),
"likes": { "$ne": ObjectId("54bb2244a3a0f26f885be2a4") }
},
{
"$inc": { "likeCount": 1 },
"$push": { "likes": ObjectId("54bb2244a3a0f26f885be2a4") }
}
)
Now the $inc operation there will increase the value of "likeCount" by the number specified, so increase by 1. The $push operation adds the unique identifier for the user to the array in the document for future reference.
The main important thing here is to keep a record of those users who voted and what is happening in the "query" part of the statement. Apart from selecting the document to update by it's own unique "_id", the other important thing is to check that "likes" array to make sure the current voting user is not in there already.
The same is true for the reverse case or "removing" the "like":
db.photos.update(
{
"_id": ObjectId("54bb201aa3a0f26f885be2a3"),
"likes": ObjectId("54bb2244a3a0f26f885be2a4")
},
{
"$inc": { "likeCount": -1 },
"$pull": { "likes": ObjectId("54bb2244a3a0f26f885be2a4") }
}
)
The main important thing here is the query conditions being used to make sure that no document is touched if all conditions are not met. So the count does not increase if the user had already voted or decrease if their vote was not actually present anymore at the time of the update.
Of course it is not practical to read an array with a couple of hundred entries in a document back in any other part of your application. But MongoDB has a very standard way to handle that as well:
db.photos.find(
{
"_id": ObjectId("54bb201aa3a0f26f885be2a3"),
},
{
"photo": 1
"likeCount": 1,
"likes": {
"$elemMatch": { "$eq": ObjectId("54bb2244a3a0f26f885be2a4") }
}
}
)
This usage of $elemMatch in projection will only return the current user if they are present or just a blank array where they are not. This allows the rest of your application logic to be aware if the current user has already placed a vote or not.
That is the basic technique and may work for you as is, but you should be aware that embedded arrays should not be infinitely extended, and there is also a hard 16MB limit on BSON documents. So the concept is sound, but just cannot be used on it's own if you are expecting 1000's of "like votes" on your content. There is a concept known as "bucketing" which is discussed in some detail in this example for Hybrid Schema design that allows one solution to storing a high volume of "likes". You can look at that to use along with the basic concepts here as a way to do this at volume.
I'm coming to CouchDB from an SQL background and am trying to do the common "SELECT FROM DB where field = someValue". I've created the following design document:
{
"_id": "_design/views",
"views": {
"byRubric": {
"map": "function(doc) {if(doc.idRubric){emit(doc._id, doc.idRubric);} }"
}
}
}
If I query the CouchDB table using the following URL, it correctly returns all 15 documents in the table:
http://localhost:5984/rubric_content/_design/views/_view/byRubric
If, however, I try to get those documents in this view which have a particular value in the idRubric field, one which I know is present by, for example, executing the following url, I get 0 documents back when, in fact, 12 of the 15 documents have this specific value in the idRubric field. http://localhost:5984/rubric_content/_design/views/_view/byRubric?key="9bf94452c27908f241ab559d2a0d46c5" (no, it doesn't make any difference if the " marks are replaced by %22). The URL does fail if I leave the quote marks off.
What am I missing? Running this locally for test on OSX 10.12.3 using couchdb - Apache CouchDB 1.6.1
Your view is emitting the document with the document with the id as the key.
Instead, you want to emit the the rubricID as the key.
{
"_id": "_design/views",
"views": {
"byRubric": {
"map": "function(doc) {if(doc.idRubric){emit(doc.idRubric);} }"
}
}
}
Then, the query will be the following :
http://localhost:5984/rubric_content/_design/views/_view/byRubric?key="rubric3"
When you use a map, you need to think as if it was a dictionnary. You have a key and a value. You will search for a matching key and get the value.
If you don't emit any value, you can simply use the ?include_docs=true parameter to get the entire document.
In a contact management app, each user will have his own database. When users wish to share certain categories of contacts with others, a backend will initiate a replication. Each contact is its own document, but also has various children documents such as notes and appointments.
Here is an example...
Contact:
{
"_id": 123,
"type": "contact",
"owner": "jimmy",
"category": "customer",
"name": "Bob Jones",
"email": "bob#example.com"
}
Note:
{
"_id": 456,
"type": "note",
"owner": "jimmy",
"contact_id": 123,
"timestamp": 1383919278,
"content": "This is a note about Bob Jones"
}
So let's say Jimmy wants to share his only his customers with sales manager Kevin, while his personal contacts remain private. When the note passes through the replication filter, is it possible to access the linked contact's category field?
Or do I have to duplicate the category field in every single child of a contact? I would prefer not to have to do this, as each contact may have many children which I would have to update manually every time the category changes.
Here is some pseudo-code for the filter function:
function(doc, req)
{
if(doc.type == “contact”) {
if(doc.category == req.query.category) {
return true;
}
}
else if(doc.contact_id) {
if(doc.contact.category == req.query.category) {
return true;
}
}
return false;
}
If this is possible, please describe how to do it. Thanks!
There are some other options.
There's a not-so-well-known JOIN trick in CouchDB. Instead of using replication, however, you'll have to share the results of a MapReduce View -- unfortunately you can use a view as a filter for replication. If you're using Cloudant (disclaimer: I'm employed by Cloudant) you can use chained-MapReduce to output the result to another database that you could then replication from...
Additionally, I think this SO post/answer on document structures and this join trick could be helpful: Modeling relationships on CouchDB between documents?
No, this is not possible. Each document must be consistent so it has no any explicit relations with others documents. Having contact_id value as reference is just an agreement from your side - CouchDB isn't aware about this.
You need to literally have category document be nested within contact one to do such trick e.g. have single document to process by filter function. This is good solution from point when you need to have consistent state of contact document.
I want to store votes in CouchDB. To get round the problem of incrementing a field in one document and having millions of revisions, each vote will be a seperate document:
{
_id: "xyz"
type: "thumbs_up"
vote_id: "test"
}
So the actual document itself is the vote. The result I'd like is basically an array of: vote_id, sumOfThumbsUp, sumOfThumbsDown
Now I think my map function would need to look like:
if(type=="thumbs_up" | type =="thumbs_down"){
emit(vote_id, type)
}
Now here's the bit I can't figure out what to do, should I build a reduce function to somehow sum the vote types, keeping in mind there's two types of votes.
Or should I just take what's been emited from the map function and put it straight into an array to work on, ignoring the reduce function completely?
This is a perfect case for map-reduce! Having each document represent a vote is the right way to go in my opinion, and will work with CouchDB's strengths.
I would recommend a document structure like this:
Documents
UPVOTE
{
"type": "vote",
"vote_id": "test",
"vote": 1
}
DOWNVOTE
{
"type": "vote",
"vote_id": "test",
"vote": -1
}
I would use a document type of "vote", so you can have other document types in your database (like the vote category information, user information, etc)
I kept "vote_id" the same
I made the value field called "vote", and just used 1/-1 instead of "thumbs_up" or "thumbs_down" (really doesn't matter, you can do whatever you want and it will work just fine)
View
Map
function (doc) {
if (doc.type === "vote") {
emit(doc.vote_id, doc.vote);
}
}
Reduce
_sum
You end up with a result like this for your map function:
And if you reduce it:
As you add more vote documents with more vote_id variety, you can query for a specific vote_id by using: /:db/_design/:ddoc/_view/:view?reduce=true&group=true&key=":vote_id"