If I have the following tables
Post - id, title, content, categoryId
Category - id, name
And some categories don't have posts linked to them, how can I select only the categories that are referenced from the Posts table
I found this in their github issues, but its code from V1, which no longer works, however it demonstrates, I think, what I would like to accomplish
ModelA.findAll({
include: [ModelB],
having: 'count(ModelB.id) > 0'
});
If ModelB is referenced one or more times in ModelA, include it.
Edit: I don't really want to include it, as I only need the data from the Category table, and not the Posts table.
I'm using postgres, if it matters.
required tag helps you in this.
ModelA.findAll({
include: [{
model: ModelB,
required: true
]
});
This will only return rows in ModelA which have at least one corresponding entry in ModelB
Related
What is the advantage of defining relationships in sequilizejs on a given modal , is it just for the purpose of more succinct queries ? I do see an example such as (Found HERE) :-
User.hasMany(Picture)
User.belongsTo(Picture, { as: 'ProfilePicture', constraints: false })
user.getPictures() // gets you all pictures
user.getProfilePicture() // gets you only the profile picture
User.findAll({
where: ...,
include: [
{ model: Picture }, // load all pictures
{ model: Picture, as: 'ProfilePicture' }, // load the profile picture. Notice that the spelling must be the exact same as the one in the association
]
})
Does having a relationship defined avaoid the usage of too many queries with the include param ? I.E. does the below :-
user.getPictures() // gets you all pictures
user.getProfilePicture() // gets you only the profile picture
Do away with the more verbose :-
User.findAll({
where: ...,
include: [
{ model: Picture }, // load all pictures
{ model: Picture, as: 'ProfilePicture' }, // load the profile picture. Notice that the spelling must be the exact same as the one in the association
]
})
I am using sequilizejs in an already existing project so the models were not created by me and hence an trying to understand the advantage of having relationships such as belongsTo and hasOne being defined in a model. Would appreciate any insight into the same.
P.S. I do see a more detailed documentation HERE
Also , as a secondary question what are the other advantages of using relationships in a db ?
Defining the relationships is actually required to be able to use include in the queries.
By using include, Sequelize will create a JOIN query, so you can get data from multiple collections which are linked by relationships without the need of a second query.
When using belongsTo, hasOne, hasMany etc. these methods are creating aditional columns in the table to create the relationships between the tables.
I'm new to mongodb and to overall databases side of development.
I'm trying to make a product listing site where all the categories would be displayed with the number of products within that particular category and when clicked on a particular category, it would get me all the products in that category.
Some things to note are:
every product will have only one category
each category will have multiple products
I don't know how to go about this problem and tried searching it online but couldn't exactly find what I was looking for. I've also tried making the schema for this but I do not know if it's the right approach or not and this is how it looks:
const productsSchema = {
category: String,
name: String,
price: String,
description: String,
thumbnail: String,
};
Side note: I'm using MERN stack.(if its of any help)
If I've understand well your question, you can use something like this:
db.collection.aggregate([
{
"$match": {
"category": "category1"
}
},
{
"$count": "total"
}
])
With this query you will get the total $count for each category.
Example here
In your frontend you will need a call for every category.
Maybe if your DB has a lot of different categories this is not a good approach, but if the number is not large enough you can call this query a couple times and you will get the result you want.
MongoDB Documentation reference here
I would say you should have a product schema and a product category schema, where the product category schema has an array of product ids that belong to that category.
In the product schema, you could also have a pointer to the category object that a product is linked to (as opposed to just the name of the category as a string).
Maybe take a look at mongoose populate https://mongoosejs.com/docs/populate.html
Designing a PostgreSQL database that will be queried by a Node API using Sequelize. Currently, I have a table called recipes that has columns called ingredients and instructions. Those columns are stored for a given as an array of strings like {Tomatoes, Onions}.
That method of storage worked fine for simply fetching and rendering a recipe on the client side. But it wasn't working well for fuzzy search querying because, using Sequelize all I could do was ingredients: { [Op.contains] : [query] }. So if a user typed tomatoes there was no way to write a "fuzzy" search query that would return a recipe with an ingredient Tomatoes.
And then I read this in the PostgreSQL documentation:
Arrays are not sets; searching for specific array elements can be a sign of database misdesign. Consider using a separate table with a row for each item that would be an array element. This will be easier to search, and is likely to scale better for a large number of elements.
Now I'm considering storing ingredients and instructions as separate tables, but I have a couple of questions.
1) As a recipe can have multiple ingredients related to it, should I just use a foreign key for each ingredient and the Sequelize hasMany relationship? That seems correct to me, except that I'm now potentially duplicating common ingredients each time a new recipe is created that uses that ingredient.
2) What would be the best way to write a fuzzy search query so that a user could search the main columns of the recipes table (e.g. title, description) and additionally apply their query to the instructions and ingredients tables?
Essentially I'd like to end up with a fuzzy search query applied to the three tables that looks something like this...
const recipes = await req.context.models.Recipe.findAll({
where: {
[Op.or]: [
{ title: { [Op.iLike]: '%' + query + '%' } },
{ description: { [Op.iLike]: '%' + query + '%' } },
{ ingredients: { ingredient: { [Op.iLike]: '%' + query + '%' } } },
{ instructions: { instruction: { [Op.iLike]: '%' + query + '%' } } }
]
}
});
Thanks!
I have done this, i happen to use graphql in my node layer with sequelize, and i have filter objects that do this type of thing. You'll just need some include statements in your Recipie.findAll.. after your initial where clause where you evaluate whether you are searching title or description or both type thing. i sent my search params in with prefix's i could strip off that told me what sequelize op's i would want to use on them and just ran my args through a utility method to create my where clause, but i know there are many ways to skin that cat. i just did not want to clutter up my resolvers with tonnes of hardcoded ops and conditional clauses was all.... your include might look something like this
include: [{
model: models.Ingredient,
as: 'Ingredients',
through: { some join table specifying keys where necessary since this
is many to many }
where: {some conditional code around your search param},
}, {
model: models.Instruction,
as: 'Instructions',
where: {some conditional code around your search param},
}],
There is good documentation around multiple includes, or nested includes in the sequelize docs, but from what i see above you have a fairly good understanding of what you need to do. To uncomplicate things a bit, i'd start with just searching on your fields from recipie (title, description) before you add the includes and get that working, then it will be a little clearer how you want to form your where clauses.
alternativley.. you can skip the includes and write associations in your models and call them with getters and pass the where clauses to those... i do that as well and again well documented stuff now.. Sequelize has really upped their game
Recipie.associate = function (models) {
models.Recipie.hasMany(models.Ingredient, { as: 'Ingredients', through: "recipie_ingredient" foreignKey: 'recipie_id'});
};
now you have a getter for Ingredients, and if you declare belongsToMany targetting back at Recipie in the Ingredient model then you'll have a getter there as well, and you can pass your search string to that via where clause and get all recipies that have a given ingredient or ingredient list type thing.... Clear as mud?
I am trying to add order in the query but to be based on condition.
The goal is to order users that are in a relation but based on a flag they have
Include in the main query has properties like this
include: { model: User, include: { model: User, as: 'parent' } }
Now on the client, I have 2 columns in the table that have the same property name, but one has property parent and the other does not.
example:
order: [[ { model: User }, 'name', sorting ]]
When I do ordering like above I am sorting with name property but including both User and User as a parent. Is there a way that I can separate these two?
I saw in the docs that sorting is possible with using sequelize.fn but can't find any examples with it. Can anyone help?
To order the parent association which is it a User as well you can do the following
[[‘name’, sorting], [{model: User, as: 'Parent'}, 'name', sorting]]
That should work and hope will help you !
I'm playing with model associations in sails and I'm curious if it's possible to make a query base on the associated field.
Example:
User.js
attributes:{
classes: { collection: 'Class', via: 'students' }
}
Class.js
attributes: {
type: ...
students: { collection: 'User', via: 'classes'}
}
Is there a way to retrieve specific Classes of a Student base on the type of class because right now everything is being returned when I use .populate(). (maybe similar with the logic below)
User
.findOne({name: 'StudentA'})
.populate('classes')
.where({'classes.type':['type1', 'type2']})
.then(....)
Thanks
You can add a where clause to your populate like so:
User
.findOne({name: 'StudentA'})
.populate('classes', {where: {type: ['type1', 'type2']}})
.exec(...)
In addition to where, you can also use skip, limit and sort in the second argument to populate.
Keep in mind this is still (as of this posting) in beta, so if you find any issues where it seems to not be working correctly, please post them to the Waterline GitHub issues forum.