I am migrating an application from mySQL to couchDB. (Okay, Please dont pass judgements on this).
There is a function with signature
getUserBy($column, $value)
Now you can see that in case of SQL it is a trivial job to construct a query and fire it.
However as far as couchDB is concerned I am supposed to write views with map functions
Currently I have many views such as
get_user_by_name
get_user_by_email
and so on. Can anyone suggest a better and yet scalable way of doing this ?
Sure! One of my favorite views, for its power, is by_field. It's a pretty simple map function.
function(doc) {
// by_field: map function
// A single view for every field in every document!
var field, key;
for (field in doc) {
key = [field, doc[field]];
emit(key, 1);
}
}
Suppose your documents have a .name field for their name, and .email for their email address.
To get users by name (ex. "Alice" and "Bob"):
GET /db/_design/example/_view/by_field?include_docs=true&key=["name","Alice"]
GET /db/_design/example/_view/by_field?include_docs=true&key=["name","Bob"]
To get users by email, from the same view:
GET /db/_design/example/_view/by_field?include_docs=true&key=["email","alice#gmail.com"]
GET /db/_design/example/_view/by_field?include_docs=true&key=["name","bob#gmail.com"]
The reason I like to emit 1 is so you can write reduce functions later to use sum() to easily add up the documents that match your query.
Related
I find myself doing a lot of queries to fetch just the first couple of items of a big set, e.g. to show the three most recent news articles or blog posts on the homepage of a website.
As long as this query only involves predefined or custom Parts, I can do something like this:
public IEnumerable<ContentItem> GetTopArticles(int amount)
{
var cultureRecord = _cultureManager.GetCultureByName(_orchardServices.WorkContext.CurrentCulture);
var articles = _orchardServices.ContentManager.Query().ForType("Article")
.Where<LocalizationPartRecord>(lpr => lpr.CultureId == cultureRecord.Id)
.OrderBy<CommonPartRecord>(cpr => cpr.PublishedUtc)
.Slice(0, amount);
return articles;
}
I'm assuming this will more or less be the same as a SELECT TOP [amount] ... in SQL and will have good performance on a large number of records.
However, sometimes I use Migrations or Import to create Content Types from an external source and want to conditionally check a field from the generic Part. In this case I don't have a Part or PartRecord class that I can pass as a parameter to the ContentQuery methods and if I want to do a conditional check on any of the fields I currently do something like this:
public IEnumerable<ContentItem> GetTopArticles(int amount)
{
var articles = _orchardServices.ContentManager.Query().ForType("Article")
.OrderBy<CommonPartRecord>(cpr => cpr.PublishedUtc)
.List()
.Where(a => a.Content.Article.IsFeatured.Value == true)
.Take(amount);
return articles;
}
This is really wasteful and causes large overhead on big sets but I really, REALLY, do not want to delve into the database to figure out Orchard's inner workings and construct long and complex HQL queries every time I want to do something like this.
Is there any way to rewrite the second query with IContentQuery methods without incurring a large performance hit?
I'm working on something similar (being able to query model data with a dynamic name). Sadly, I haven't found anything that makes it easy.
The method I've found that works is to do plain SQL queries against the database. Check out this module for syntax on that if you do later find yourself willing to delve into the database.
I have a use case where I have to remove a subset of entities stored in couchbase, e.g. removing all entities with keys starting with "pii_".
I am using NodeJS SDK but there is only one remove method which takes one key at a time: http://docs.couchbase.com/sdk-api/couchbase-node-client-2.0.0/Bucket.html#remove
In some cases thousands of entities need to be deleted and it takes very long time if I delete them one by one especially because I don't keep list of keys in my application.
I agree with the #ThinkFloyd when he saying: Delete on server should be delete on server, rather than requiring three steps like get data from server, iterate over it on client side and finally for each record fire delete on the server again.
In this regards, I think old fashioned RDBMS were better all you need to do is 'DELETE * from database where something=something'.
Fortunately, there is something similar to SQL is available in CouchBase called N1QL (pronounced nickle). I am not aware about JavaScript (and other language syntax) but this is how I did it in python.
Query to be used: DELETE from <bucketname> b where META(b).id LIKE "%"
layer_name_prefix = cb_layer_key + "|" + "%"
query = ""
try:
query = N1QLQuery('DELETE from `test-feature` b where META(b).id LIKE $1', layer_name_prefix)
cb.n1ql_query(query).execute()
except CouchbaseError, e:
logger.exception(e)
To achieve the same thing: alternate query could be as below if you are storing 'type' and/or other meta data like 'parent_id'.
DELETE from <bucket_name> where type='Feature' and parent_id=8;
But I prefer to use first version of the query as it operates on key, and I believe Couchbase must have some internal indexes to operate/query faster on key (and other metadata).
The best way to accomplish this is to create a Couchbase view by key and then range query over that view via your NodeJS code, making deletes on the results.
http://docs.couchbase.com/admin/admin/Views/views-querySample.html
http://docs.couchbase.com/couchbase-manual-2.0/#couchbase-views-writing-querying-selection-partial
http://docs.couchbase.com/sdk-api/couchbase-node-client-2.0.8/ViewQuery.html
For example, your Couchbase view could look like the following:
function(doc, meta) {
emit(meta.id, null);
}
Then in your NodeJS code, you could have something that looks like this:
var couchbase = require('couchbase');
var ViewQuery = couchbase.ViewQuery;
var query = ViewQuery.from('designdoc', 'by_id');
query.range("pii_", "pii_" + "\u0000", false);
var myBucket = myCluster.openBucket();
myBucket.query(query, function(err, results) {
for(i in results) {
// Delete code in here
}
});
Of course your Couchbase design document and view will be named differently than the example that I gave, but the important part is the ViewQuery.range function that was used.
All document ids prefixed with pii_ would be returned, in which case you can loop over them and start deleting.
Best,
I am scraping an 90K record database using JSON-RPC and I am trying to put in some basic error checking. I want to start by scraping the database twice using two different settings and adding a prefix to the second scrape. This way I can check to ensure that the two settings are not producing different records (due to dropped updates, etc). I wanted to implement the comparison using a view which compares each document from the first scrape with it's twin produced by the second scrape and then emit the names of records with a difference between them.
However, I cannot quite figure out how to pull in another doc in the view, everything I have read only discusses external docs using the emit() function, which is too late to permit me to compare it. In the example below, the lookup() function would grab the referenced document.
Is this just not possible?
function(doc) {
if(doc._id.slice(0,1)!=='$' && doc._id.slice(0,1)!== "_"){
var otherDoc = lookup('$test" + doc._id);
if(otherDoc){
var keys = doc.value.keys();
var same = true;
keys.forEach(function(key) {
if ((key.slice(0,1) !== '_') && (key.slice(0,1) !=='$') && (key!=='expires')) {
if (!Object.equal(otherDoc[key], doc[key])) {
same = false;
}
}
});
if(!same){
emit(doc._id, 1);
}
}
}
}
Context
You are correct that this is not possible in CouchDB. The whole point of the map function is that it must be idempotent, otherwise you lose all the other nice benefits of a pre-calculated index.
This is why you cannot access external resources in the map function, whether they be other records or the clock. Any time you run a map you must always get the same result if you put the same record into it. Since there are no relationships between records in CouchDB, you cannot promise that this is possible.
Solution
However, you can still achieve your end goal, just be different means. Some possibilities...
Assuming there is some meaningful numeric value in each doc, you could use a view to take the sum of all those values and group them by which import you did ({key: <batch id>, value: <meaningful number>}). Then compare the two numbers in your client or the browser to see if they match.
A brute force approach would be to use a view to pair the docs that should match. Each doc is on a different row, but they're grouped by a common field. Then iterate through the entire index comparing the pairs. This would certainly be the quickest to code and doesn't depend on your application or data.
Implement a validation function to enforce a schema on your data. Just be warned that this will reduce your write throughput since each written record will be piped out of Erlang and into the JS engine. Also, this is only applicable if you're worried about properly formed records instead of their precise content, which might not be the case.
Instead of your different batch jobs creating different docs, have them place them into the same doc. The structure might look like this: { "_id": "something meaningful", "batch_one": { ..data.. }, "batch_two": { ..data.. } } Then your validation function could compare them or you could create a view that indexes all the docs that don't match. All depends on where in your pipeline you want to do the error checking and correction.
Personally I like the last option better, but only if you don't plan to use the database as is in production. Ie., you wouldn't want to carry around all that extra data in each record.
Hope that helps.
Cheers.
As the question suggests, I need to find out how to access entity data that has been passed into a JavaScript function via a lookup.
JavaScript Code Follows:
// function to generate the correct Weighting Value when these parameters change
function TypeAffectedOrRegionAffected_OnChanged(ExecutionContext, Type, Region, Weighting, Potential) {
var type = Xrm.Page.data.entity.attributes.get(Type).getValue();
var region = Xrm.Page.data.entity.attributes.get(Region).getValue();
// if we have values for both fields
if (type != null && region != null) {
// create the weighting variable
var weighting = type[0].name.substring(4) + "-" + region;
// recreate the Weighting Value
Xrm.Page.data.entity.attributes.get(Weighting).setValue(weighting);
}
}
As you can see with the following line using the name operator I can access my Type entity's Type field.
// create the weighting variable
var weighting = type[0].name.substring(4) + "-" + region;
I am looking for a way now to access the values stored inside my type object. It has the following fields new_type, new_description, new_value and new_kind.
I guess I'm looking for something like this:
// use value of entity to assign to our form field
Xrm.Page.data.entity.attributes.get(Potential).setValue(type[0].getAttribute("new_value"));
Thanks in advance for any help.
Regards,
Comic
REST OData calls are definitely the way to go in this case. You already have the id, and you just need to retrieve some additional values. Here is a sample to get you started. The hardest part with working with Odata IMHO is creating the Request Url's. There are a couple tools, that you can find on codeplex, but my favorite, is actually to use LinqPad. Just connect to your Org Odata URL, and it'll retrieve all of your entities and allow you to write a LINQ statement that will generate the URL for you, which you can test right in the browser.
For your instance, it'll look something like this (it is case sensitive, so double check that if it doesn't work):
"OdataRestURL/TypeSet(guid'" + type[0].Id.replace(/{/gi, "").replace(/}/gi, "") + "'select=new_type,new_description,new_value,new_kind"
Replace OdataRestURL with whatever your odata rest endpoint is, and you should be all set.
Yes Guido Preite is right. You need to retrieve the entity by the id which come form the lookup by Rest Sync or Async. And then get Json object. However for make the object light which is returned, you can mention which fields to be backed as part of the Json. Now you can access those fields which you want.
I'm tryting to decide the best approach for a CouchApp (no middleware). Since there are similarities to my idea, lets assume we have a stackoverflow page stored in a CouchDB. In essence it consists of the actual question on top, answers and commets. Those are basically three layers.
There are two ways of storing it. Either within a single document containing a suitable JSON representation of the data, or store each part of the entry within a separate document combining them later through a view (similar to this: http://www.cmlenz.net/archives/2007/10/couchdb-joins)
Now, both approaches may be fine, yet both have massive downsides from my current point of view. Storing a busy document (many changes through multiple users are expected) as a signle entity would cause conflicts to happen. If user A stores his/her changes to the document, user B would receive a conflict error once he/she is finished typing his/her update. I can imagine its possible to fix this without the users knowledge through re-downloading the document before retrying.
But what if the document is rather big? I'll except them to become rather blown up over time which would put quite some noticeable delay on a save process, especially if the retry process has to happen multiple times due to many users updating a document at the same time.
Another problem I'd see is editing. Every user should be allowed to edit his/her contributions. Now, if they're stored within one document it might be hard to write a solid auth handler.
Ok, now lets look at the multiple documents approach. Question, Answers and Comments would be stored within their own documents. Advantage: only the actual owner of the document can cause conflicts, something that won't happen too often. Being rather small elements of the whole, redownloading wouldn't take much time. Furthermore the auth routine should be quite easy to realize.
Now here's the downside. The single document is real easy to query and display. Having a lot of unsorted snippets laying around seems like a messy thing since I didn't really get the actual view to present me with a 100% ready to use JSON object containing the entire item in an ordered and structured format.
I hope I've been able to communicate the actual problem. I try to decide which solution would be more suitable for me, which problems easier to overcome. I imagine the first solution to be the prettier one in terms of storage and querying, yet the second one the more practical one solvable through better key management within the view (I'm not entirely into the principle of keys yet).
Thank you very much for your help in advance :)
Go with your second option. It's much easier than having to deal with the conflicts. Here are some example docs how I might structure the data:
{
_id: 12345,
type: 'question',
slug: 'couchdb-single-document-vs-joining-documents-together',
markdown: 'Im tryting to decide the best approach for a CouchApp (no middleware). Since there are similarities to...' ,
user: 'roman-geber',
date: 1322150148041,
'jquery.couch.attachPrevRev' : true
}
{
_id: 23456,
type: 'answer'
question: 12345,
markdown: 'Go with your second option...',
user : 'ryan-ramage',
votes: 100,
date: 1322151148041,
'jquery.couch.attachPrevRev' : true
}
{
_id: 45678,
type: 'comment'
question: 12345,
answer: 23456,
markdown : 'I really like what you have said, but...' ,
user: 'somedude',
date: 1322151158041,
'jquery.couch.attachPrevRev' : true
}
To store revisions of each one, I would store the old versions as attachments on the doc being edited. If you use the jquery client for couchdb, you get it for free by adding the jquery.couch.attachPrevRev = true. See Versioning docs in CouchDB by jchris
Create a view like this
fullQuestion : {
map : function(doc) {
if (doc.type == 'question') emit([doc._id, null, null], null);
if (doc.type == 'answer') emit([doc.question, doc._id, null], null);
if (doc.type == 'comment') emit([doc.question, doc.answer, doc._id], null) ;
}
}
And query the view like this
http://localhost:5984/so/_design/app/_view/fullQuestion?startkey=['12345']&endkey=['12345',{},{}]&include_docs=true
(Note: I have not url encoded this query, but it is more readable)
This will get you all of the related documents for the question that you will need to build the page. The only thing is that they will not be sorted by date. You can sort them on the client side (in javascript).
EDIT: Here is an alternative option for the view and query
Based on your domain, you know some facts. You know an answer cant exist before a question existed, and a comment on an answer cant exist before an answer existed. So lets make a view that might make it faster to create the display page, respecting the order of things:
fullQuestion : {
map : function(doc) {
if (doc.type == 'question') emit([doc._id, doc.date], null);
if (doc.type == 'answer') emit([doc.question, doc.date], null);
if (doc.type == 'comment') emit([doc.question, doc.date], null);
}
}
This will keep all the related docs together, and keep them ordered by date. Here is a sample query
http://localhost:5984/so/_design/app/_view/fullQuestion?startkey=['12345']&endkey=['12345',{}]&include_docs=true
This will get back all the docs you will need, ordered from oldest to newest. You can now zip through the results, knowing that the parent objects will be before the child ones, like this:
function addAnswer(doc) {
$('.answers').append(answerTemplate(doc));
}
function addCommentToAnswer(doc) {
$('#' + doc.answer).append(commentTemplate(doc));
}
$.each(results.rows, function(i, row) {
if (row.doc.type == 'question') displyQuestionInfo(row.doc);
if (row.doc.type == 'answer') addAnswer(row.doc);
if (row.doc.type == 'comment') addCommentToAnswer(row.doc)
})
So then you dont have to perform any client side sorting.
Hope this helps.