I am new to pouchdb and I am reading below source code:
db.query('product_index', {
startkey: ["01234"],
endkey: ["01234", {}],
include_docs: false
});
this code executes for a long time. After read some pouchdb document it looks like it builds index on the database when it run the first time. But I don't understand which fields are indexed based on above code.
Below code I can see it builds index on field foo. But how can I understand query API for building index? What is the different between using query and createIndex from index perceptive?
db.createIndex({
index: {
fields: ['foo']
}
})
Have you seen the PouchDB Guide Bulk operations section Please use 'allDocs()'. Seriously.?
Far too many developers overlook this valuable API, because they
misunderstand it. When a developer says "my PouchDB app is slow!", it
is usually because they are using the slow query() API when they
should be using the fast allDocs() API.
When designing your data structures it's very important to bear that in mind. You should define your record id fields to optimize data accessibility through allDocs().
Related
I recently started using Node.js + Express.js (generated with pug) + pg-promise for handling db.
My first target is to obtain data from Postgres (already set up) and display it pretty using render and pug. Let's say it is user list from Users table.
On this restful tutorial I have learned how to get data and return it as JSON - it worked.
Based on Mozilla's tutorial I seperated my code:
routes/users.js: where for '/' I call user_controller.user_list method (using router.get)
controllers/userController.js I have exported user_list where I would like to ask model for data and call render if I have results
queries.js which is kinda my model? But I'm not sure. It has API: connection to db with promises and one function for every query I am going to use in Controllers. I believe I should have like one Model file per table (or any logical entity) but where to store pgp connections?
This file is based on first tutorial I mentioned
// queries.js (connectionString is set properly to my postgres)
var pgp = require('pg-promise')(options);
var db = pgp(connectionString);
function getUsers(req, res, next) {
db.any('SELECT (user_id, username) FROM public.users ORDER BY user_id ASC LIMIT 1000')
.then(function (data) {
res.json({ data: data });
})
.catch(function (err) {
return next(err);
});
}
module.exports = {
getUsers: getUsers
};
Here starts my problem as most tutorials uses mongoose which is very model-db-schema-friendly and what I have is simple 'SELECT ...' string I pass to pg-promise's any() function.
Therefore I have no model class like User.
In userControllers.js I don't know how to call getUsers() to handle its data. Returning JS object from getUsers() would be nice.
Also: where should I call render? In controller or only in
db.any(...).then(function (data) { <--here--> })
Before, I also tried to embed whole Postgres handling into Controller but from db.any() I got this array for handling:
[{ row: '(1,John)' },{ row: '(2,Amy)' },{ row: '(50,Peter)' } ]
Didn't know how go from there as I probably lost my API functionality as well ;-)
I am browsing through multiple tutorials how to handle MVC but usually they handle MongoDB and
satisfy readers with res.send() not render().
I am not sure that I understand what your question is exactly about, but since I do not have enough reputation to comment, I'll do my best to help you with your interrogations. :)
First, regarding the queries.js file, it is IMO not exactly a model, but rather a DAO (Data Access Object) file. DAO comes between you Model (which is actually you database) and your Controller layers. There usually is a DAO file per object (User, Pet, whatever you want) in your data model.
When the data model is rather complex, it can be useful to use an Object Relational Mapping (ORM) such as Mongoose to map your database and execute complexe processes on your objects. In such a case, you might need a specific file per object so as to describe your model and store your queries. But since you don't need an ORM, you DAO can directly interact with your database. That is why you do not have a User.js file.
Regarding the way the db object should be used, I think you should refer directly to pg-promise documentation on the matter.
IMPORTANT: For any given connection, you should only create a single
Database object in a separate module, to be shared in your application
(see the code example below). If instead you keep creating the
Database object dynamically, your application will suffer from loss in
performance, and will be getting a warning in a development
environment (when NODE_ENV = development)
As a matter of fact, a db object in pg-promise sort of represents the database itself and is actually designed for the simultaneous use of several databases, which does not seem to be your case for the moment.
Finally, when it comes to the render function, I believe it should be in the controller, as your DAO is not supposed to know how the data it has gathered is going to be used.
Modularity is always a time-saving choice on the long-term.
Furthermore, note that you might later need a Business Layer between your DAO and your controller, in order to preprocess and postprocess data you are going to persist or to display. In such a case, if you need for instance to ask for data from your database, you will need to render data after it is processed by the Business layer. If the render is made in the DAO layer, it will not be possible.
In the link I provided earlier to pg-promise's db object connection, you will also find documentation on the any() method. You might already have looked it up.
It specifically states that it returns
A promise object that represents the query result:
When no rows are returned, it resolves with an empty array.
When 1 or more rows are returned, it resolves with the array of rows.
so your returned data is a JS Array. If you want to make it a JS object, just use
JSON.stringify(yourArray) to process your data before rendering it in your controller.
But I wonder if Pug is not able to use your data directly.
Also, if you cannot get any data out of your DAO, maybe you should check that your data object is not empty, as such a case is tolerated by the any() method. If you expect your query to always return something, you might want to consider using the many() or the one() methods.
I hope this helps you.
I’m trying to understand what the advantages are of GraphQL. I’ve read about reducing the number of endpoints and the complexity of server responses, but it seems that the same results can be achieved with JS alone.
Here’s an example of a data object that could be sent as JSON to a node server with MongoDB. This would be an example of a game app where the client is retrieving user info:
let data = {
db: "users",
params: {_id: "xxxxx"},
fields: ["username", "level"],
games:
{
db: "games",
params: {userID: "xxxxx"},
fields: ["opponent”]
}
}
In this example, db, params, and fields would be standard keys, and games would be like a special key for the specific purpose of retrieving the user’s games, however, the syntax of the games object would follow the same standard format as the overall data object.
Then on the server, the Mongo query would look something like this:
db.collection(data.db).find(params)
You’d then filter out the extraneous Mongo fields in some standardized way and respond to the client.
I’m a relative beginner with JS, but I think you could also chain promises based on whether certain special keys (e.g., “games” from above) are included in the data object.
This seems like it achieves the same benefits as GraphQL with less complexity. What other benefits does GraphQL have that a plain JS equivalent does not?
I'm using an ajax request from the front end to load more comments to a post from the back-end which uses NodeJS and mongoose. I won't bore you with the front-end code and the route code, but here's the query code:
Post.findById(req.params.postId).populate({
path: type, //type will either contain "comments" or "answers"
populate: {
path: 'author',
model: 'User'
},
options: {
sort: sortBy, //sortyBy contains either "-date" or "-votes"
skip: parseInt(req.params.numberLoaded), //how many are already shown
limit: 25 //i only load this many new comments at a time.
}
}).exec(function(err, foundPost){
console.log("query executed"); //code takes too long to get to this line
if (err){
res.send("database error, please try again later");
} else {
res.send(foundPost[type]);
}
});
As was mentioned in the title, everything works fine, my problem is just that this is too slow, the request is taking about 1.5-2.5 seconds. surely mongoose has a method of doing this that takes less to load. I poked around the mongoose docs and stackoverflow, but didn't really find anything useful.
Using skip-and-limit approach with mongodb is slow in its nature because it normally needs to retrieve all documents, then sort them, and after that return the desired segment of the results.
What you need to do to make it faster is to define indexes on your collections.
According to MongoDB's official documents:
Indexes support the efficient execution of queries in MongoDB. Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.
-- https://docs.mongodb.com/manual/indexes/
Using indexes may cause increased collection size but they improve the efficiency a lot.
Indexes are commonly defined on fields which are frequently used in queries. In this case, you may want to define indexes on date and/or vote fields.
Read mongoose documentation to find out how to define indexes in your schemas:
http://mongoosejs.com/docs/guide.html#indexes
TLDR
Is there a way to limit queryByExample to a collection in NodeJS?
Problem faced
I have a complex query with some optional fields (i.e. sometimes some search fields will be omitted). So I need to create a query dynamically, e.g. in JSON. QueryByExample seems to be the right tool to use here as it gives me that flexibility to pass a JSON. However my problem is that I would like to limit my search to only one collection or directory.
e.g. I was hoping for something like
searchJSON = {
title: { $word: "test" },
description: { $word: "desc" }
};
//query
db.documents.query(qb.where(
qb.collection("collectionName"),
qb.byExample(searchJSON)
)).result()...
In this case searchJSON could have been built dynamically, for example maybe sometimes title may be omitted from the search.
This doesn't work because the query builder only allows queryByExample to be the only query. But I'd instead like to built a dynamic search query which is limited to a collection or directory.
At present, I think you would have to express the query with QueryBuilder instead of Query By Example using
qb.and([
qb.collection('collectionName'),
qb.word('title', 'test'),
qb.word('description', 'desc')
])
See http://docs.marklogic.com/jsdoc/queryBuilder.html#word
That said, it should be possible for the Node.js API to relax that restriction based on the fixes in MarkLogic 9.0-2
Please file an issue on https://github.com/marklogic/node-client-api
I am creating an expressjs api and using mongodb. I have a decent understanding of indexes and I understand that they are expensive to create when there is data in the database.
In MS Sql Server you would create indexes when creating your database tables. My question is do I handle this creation of indexes in a post call in my express app or do I achieve this using scripts when deploymening my application?
For example I need Geospatial indexing.
Would index creation be handled in the express app like this?
//express post call
let col = db.collection( 'collection' );
col.createIndex( // someIndex );
col.insertOne( //Some document );
I am looking for the best method to creating the 'initial' state of my mongodb and specifically creating indexes I will need for certain collections before these collections contain any documents.
So, It may happen, You have a lot of data in your database while deployment and you do not want your Indexing terrible. Here's what MongoDB can Help. You can do indexing in Background which will not prevent all read and write operations to the database while the index builds.A simple Command:
db.collection.createIndex( { a: 1 }, { background: true } )
Check the Manual For details.
https://docs.mongodb.org/manual/tutorial/build-indexes-in-the-background/