I'm working with two tables in particular. Users and Friends. Users has a bunch of information that defines the User whereas Friends has two columns aside from id: user_id and friend_id where both of them are a reference to the User table.
I'm trying to find all of the users friends in as little calls to the db as possible and I currently have 2. One to retrieve the id of a user first from a request, then another to Friends where I compare the IDs from the first call and then a third call that passes the array of friends and find all of them in the Users table. This already feels like overkill and I think that with associations, there has to be a better way.
Modification of the tables unfortunately is not an option.
One thing that I saw from "http://docs.sequelizejs.com/manual/querying.html#relations---associations"
I tried but got an interesting error.. when trying to repurpose the code snippet in the link under Relations/Associations, I get "user is associated to friends multiple times. To identify the correct association, you must use the 'as' keyword to specify the alias of the association you want to include."
const userRecord = await User.findOne({
where: { id }
})
const friendsIDs = await Friends.findAll({
attributes: ["friend_id"],
where: {
user_id: userRecord.id
}
}).then(results => results.map(result => result.friend_id));
const Sequelize = require("sequelize");
const Op = Sequelize.Op;
return await User.findAll({
where: {
id: { [Op.in]: friendsIDs }
},
});
Above for my use case works. I'm just wondering if there are ways to cut down the number of calls to the db.
Turns out Sequelize handles this for you if you have the proper associations in place so yes, it was a one liner user.getFriends() for me.
Related
I'm trying to create a friendship mechanic for my app using Prisma among other tools. In the docs it shows the following example for how to create a many-to-many self relation:
model User {
id Int #id #default(autoincrement())
name String?
followedBy Follows[] #relation("following")
following Follows[] #relation("follower")
}
model Follows {
follower User #relation("follower", fields: [followerId], references: [id])
followerId Int
following User #relation("following", fields: [followingId], references: [id])
followingId Int
##id([followerId, followingId])
}
I have implemented this and it works, however the issue is that for friendships, there is no 'following' and 'followedBy', you're just friends. At the moment, when I query, I have to query both fields in order to find all of a user's friends. Is there any way to define this type of relationship with only one field? Whereby we just have a single list of friends on a user?
I agree that it would be nice if Prisma could more natively support this sort of self-relation where the relationship is expected to be symmetric (e.g. userA is friends with userB if and only if userB is friends with userA).
However, as far as I can tell Prisma insists on having two "sides" of the relationship. (If someone knows better, I would love to hear it!) So what follows is the approach I am taking, which avoids having to query both relations to find a user's full set of friends.
Concept
We'll use one "side" of the relation to contain the complete set of friends. The other "side" exists solely to meet Prisma's requirement, and we'll never query it directly.
When adding or removing a friend relationship, we'll make two prisma calls, one to update each object.
Code
Schema file:
model User {
id Int #id #default(autoincrement())
name String?
friends User[] #relation("UserFriends")
// This second "side" of the UserFriends relation exists solely
// to satisfy prisma's requirements; we won't access it directly.
symmetricFriends User[] #relation("UserFriends")
}
Methods to add and remove friendships (there's plenty of redundant code in here that could be abstracted out, but I think it's clearer to read this way):
const addFriendship = async (userIdA: string, userIdB: string) => {
await prisma.user.update({
where: {id: userIdA},
data: {friends: {connect: [{id: userIdB}]}},
});
await prisma.user.update({
where: {id: userIdB},
data: {friends: {connect: [{id: userIdA}]}},
});
};
const removeFriendship = async (userIdA: string, userIdB: string) => {
await prisma.user.update({
where: {id: userIdA},
data: {friends: {disconnect: [{id: userIdB}]}},
});
await prisma.user.update({
where: {id: userIdB},
data: {friends: {disconnect: [{id: userIdA}]}},
});
}
With this approach, one can load a user and get all their friends in the expected manner, e.g.
const getUserWithFriends = async (userId) =>
await prisma.user.find({
where: {id: userId},
include: {friends: true},
});
I have models for Users, Projects and Tasks
Users and Tasks has association Many-to-Many
Projects and Tasks has association One-to-Many (each Project has many Tasks)
When receiving Tasks for specified User, I want to get associated Project for each task.
May anybody help to find solution how yo to this.
My code is below:
// receiving of user from database
const user = await User.findOne({where: {id: request.userId}})
// receiving of tasks related to user
const tasks = await user.getTasks(
// here i've tried to add following code, but it does not works
include: { model: Project, as: 'project' }
)
response.status(201).json( tasks )
Any help would be thankful
In Sequelize, when dealing with 'many' associations, might become a little different. You said you already have this association:
Project.model
Project.hasMany(Task)
Now you need to implement the other way inside your Task.model:
Task.belongsTo(Project);
In the Sequelize Documentation you'll find this:
To create a One-To-Many relationship, the hasMany and belongsTo
associations are used together;
I have fixed problem. Correct code below.
const user = await User.findByPk( request.userId )
if(!user) return
const tasks = await user.getTasks(
{ include: [
{ model: Project, as: 'project' }
] }
)
I think I've done enough research on this subject and I've only got a headache.
Here is what I have done and understood: I have restructured my MySQL database so that I will keep my user's data in different tables, I am using foreign keys. Until now I only concluded that foreign keys are only used for consistency and control and they do not automatize or do anything else (for example, to insert data about the same user in two tables I need to use two separate insert statements and the foreign key will not help to make this different or automatic in some way).
Fine. Here is what I want to do: I want to use Sequelize to insert, update and retrieve data altogether from all the related tables at once and I have absolutely no idea on how to do that. For example, if a user registers, I want to be able to insert the data in the table "A" containing some user information and in the same task insert in the table B some other data (like the user's settings in the dedicated table or whatever). Same with retrievals, I want to be able to get an object (or array) with all the related data from different tables fitting in the criteria I want to find by.
Sequelize documentation covers the things in a way that every thing depends on the previous one, and Sequelize is pretty bloated with a lot of stuff I do not need. I do not want to use .sync(). I do not want to use migrations. I have the structure of my database created already and I want Sequelize to attach to it.
Is it possible insert and retrieve several rows related at the same time and getting / using a single Sequelize command / object? How?
Again, by "related data" I mean data "linked" by sharing the same foreign key.
Is it possible insert and retrieve several rows related at the same
time and getting / using a single Sequelize command / object? How?
Yes. What you need is eager loading.
Look at the following example
const User = sequelize.define('user', {
username: Sequelize.STRING,
});
const Address = sequelize.define('add', {
address: Sequelize.STRING,
});
const Designation = sequelize.define('designation', {
designation: Sequelize.STRING,
});
User.hasOne(Address);
User.hasMany(Designation);
sequelize.sync({ force: true })
.then(() => User.create({
username: 'test123',
add: {
address: 'this is dummy address'
},
designations: [
{ designation: 'designation1' },
{ designation: 'designation2' },
],
}, { include: [Address, Designation] }))
.then(user => {
User.findAll({
include: [Address, Designation],
}).then((result) => {
console.log(result);
});
});
In console.log, you will get all the data with all its associated models that you want to include in the query
Using sails 0.10.5/waterline 0.10.15:
I cannot find an answer to a simple question: how to count the elements of an association without using populate() (which would load all data).
Let take a simple many2many relation with via:
User:
attributes: {
following: {
collection: 'user',
via: 'follower',
dominant: true
},
follower: {
collection: 'user',
via: 'following'
}
Now I need the size of the collections.
Currently I try
User.findById(1).populateAll().exec(function(err, user) {
// count of followings -> user.following.length;
// count of followers-> user.follower.length;
}
which leads to loading the collections.
I'm missing a count function at collection level to avoid population/loading of data.
Is there a possibility to access the (auto generated) join tables to run a count-query directly on the join?
Something like:
User.findById(1).count({'followings'}).exec(function(err, followings) {
...}
or
UserFollowingFollow_FollowFollowing.countByUserFollowingFollowId(1).
exec(function(err, followings) {
...}
Waterline does offer the count query method and it can be used like this to solve your problem:
User.count().where({follower: followerId})
.exec(function(err, numberOfFollowings) {
//numberOfFollowings will be the integer that you need
})
followerId is the id that you are passing to User.findOne() in your example.
You can also read the Waterline documentation about this.
By below reference I understood how map many to many with a relationship table
http://sequelizejs.com/docs/latest/associations#many-to-many
User = sequelize.define('User', { user_name : Sequelize.STRING})
Project = sequelize.define('Project', { project_name : Sequelize.STRING })
UserProjects = sequelize.define('UserProjects', {
status: DataTypes.STRING
})
User.hasMany(Project, { through: UserProjects })
Project.hasMany(User, { through: UserProjects })
But how to query Project 's of a User
I Tried like
User.find({where:{id:1},include,[UserProjects]})
User.find({where:{id:1},include,[Projects]})
User.find({where:{id:1},include,[UserProjects]})
User.find({where:{id:1},include,[Projects]})
But i dont get results
Sequelize created table like below
users(id,name)
projects(id,project_name)
userprojects(id,UserId,ProjectId)
I tried https://github.com/sequelize/sequelize/wiki/API-Reference-Associations#hasmanytarget-options
User.find({where:{id:1}}).success(function(user){
user.getProjects().success(function (projects) {
var p1 = projects[0] // this works fine but 2 queries required. I expect in single find. without getProjects
p1.userprojects.started // Is this project started yet?
})
})
How to get all the projects of a USER ??
You should be able to get all of the properties of the user in two different ways: using includes and getting the projects from a user instance.
Using includes the code you submitted above is almost right. This method will only make one query to the database using the JOIN operation. If you want all of the users with their corresponding projects, try:
User.findAll({include: [Project]})
You can also get the projects directly from a user instance. This will take two queries to the database. The code for this looks like
User.find(1).then(function(user) {
user.getProjects().then(function(projects) {
// do stuff with projects
});
});
Does this work for you?