I am trying to create a React/Redux app which lists books. Each book then has related books. I know I should structure my redux store in some sort of normalized fashion like so:
{
books: {
'book1id': {
title: 'Book 1',
author: 'Author 1',
relatedBooks: ['book2id', 'book3id']
},
'book2id': {
title: 'Book 2',
author: 'Author 2',
relatedBooks: ['book1id']
}
}
}
and load each book as necessary.
The issue is where to store loading/error data from the API requests? Some ideas I had were to create an object for every book such as
books: {
'book1id': {
isLoading: false,
error: null,
book: {
title: 'Book 1',
...
}
},
...
}
But that seems to detract slightly from the readability/intuitiveness of the state. Is there a better way to structure the state?
I structure my redux store so that it includes an entities object for all of my relational data and I store things specific to a page or a set of routes in separate parts of the state. My state tree might look something like this:
const state = {
entities: {
books: {
...
},
authors: {
...
},
...
},
booksPage: {
isLoading: false
}
}
Now I am keeping track of my relational state separate from the state of my UI components. I would not recommend trying to store a isLoading state in an individual entity since that entity may or may not exist. If you need more granular loading/error state on a per entity basis then rather on a set of entities you have a few options. The first option is keep a set of IDs that are currently loading. This is not a very practical solution because you can't track success or failure with an ID simply being in a set or not.
The next, better solution is to keep a map from ID to a status object that includes if an individual entity is loading, if it was successful or if it failed to load and what the errors were.
const state = {
entities: {
books: {
...
},
authors: {
...
},
...
},
booksPage: {
loading: {
book1: {
status: 'FAILED',
error: 'Network request failed.'
},
book2: {
status: 'SUCCESS',
},
book3: {,
status: 'IN_PROGRESS'
}
}
}
}
In summary, I find separating out your relational state into an entities child object while having page specific sections of state to be working quite well for me.
Related
I want to run a single query with multiple mutations, but I need to reference the data from a previous mutations is that possible?
mutation {
venue1: createVenue(data: { name: "Test Venue 1", active: true }) {
id
}
layout1: createLayout(
data: { name: "Test Layout 1", active: true, venue: { connect: (I WANT TO USE venue1) } }
) {
id
}
}
This is a over-simplification of what I'm trying to do, I'll need to use a single query to seed a DB for testing purposes, and using create instead of connect won't be enough because there are required relations and elements which require multiple relations, so it need to be lineal to fill all of those relations.
Suppose I have an array feedsArray, the example value may look like this:
this.feedsArray = [
{
id: 1,
type: 'Comment',
value: 'How are you today ?'
},
{
id: 2,
type: 'Meet',
name: 'Daily sync up'
}
]
Suppose I have registered two components: Comment and Meet, Each component has a prop setting as the following:
props: {
feed: Object
}
and the main component has the following definition:
<component v-for="feed in feedsArray" :feed="feed" :key="feed.id" :is="feed.type"></component>
As you can see, it uses is property to select different component. My question is, how to detect feed object change in the child component ? Like when I set
this.feedsArray[0] = {
id: 1,
type: 'Comment',
value: 'I am not ok'
}
How can the Comment component detect the changes ? I tried to add a watcher definition in the child component like the following:
watch: {
feed: {
handler (val) {
console.log('this feed is changed')
},
deep: true
}
},
But it doesn't work here. Anyone know how to solve this ?
Do not assign directly to an array using index - use splice() instead, otherwise JavaScript can not detect that you have changed the array.
If you want to change only the value of an already existing key of an object - then simply update it e.g. this.feeds[0].value = 'I am not okay any more';
This works for existing keys only - otherwise you have to use this.$set(this.feeds[0], 'value', 'I am not okay any more');
I want to implement a follow system between users.
For that, I want to display all of the 250 users of my app, then add a checkmark button next to the ones I already follow, and an empty button next to the ones I do not follow.
var usersRef = firebase.database().ref(‘/users’);
var followingRef = firebase.database().ref(‘/followingByUser’);
var displayedUsers = [];
// I loop through all users of my app
usersRef.once('value', users => {
users.forEach(user => {
// For each user, I check if I already follow him or not
followingRef.child(myUid).child(user.key).once('value', follow => {
if (follow.val()) {
// I do follow this user, follow button is on
displayedUsers.push({
name: user.val().name,
following: true
});
} else {
// I do not follow this user, follow button is off
displayedUsers.push({
name: user.val().name,
following: false
});
}
})
})
})
When doing that, I often (not always) get the following error: "Error: Firebase Database (4.1.3) INTERNAL ASSERT FAILED: sendRequest call when we're not connected not allowed."
Eventually, all the data is fetched, but after 10 seconds instead of 1 (without the error).
I do not believe it is an internet connection issue, as I have a very fast and stable wifi.
Is it a bad practice to nest queries like that?
If not, why do I get this error?
My data is structured as below:
users: {
userId1: {
name: User 1,
email: email#exemple.com,
avatar: url.com
},
userId2: {
name: User 2,
email: email#exemple.com,
avatar: url.com
},
...
}
followByUser: {
userId1: {
userId2: true,
userId10: true,
userId223: true
},
userId2: {
userId23: true,
userId100: true,
userId203: true
},
...
}
Your current database structure allows you to efficiently look up who each user is following. As you've found out it does not allow you to look who a user is follow by. If you also want to allow an efficient lookup of the latter, you should add additional data to your model:
followedByUser: {
userId2: {
userId1: true,
}
userId10: {
userId1: true,
},
userId223: {
userId1: true,
},
...
}
This is a quite common pattern in Firebase and other NoSQL databases: you often expand your data model to allow the use-cases that your app needs.
Also see my explanation on modeling many-to-many relations and the AskFirebase video on the same topic.
I'm trying to esatblish a One-To-Many relationship between the tables: Exam and Exam_Questions, using Sequelize.
Even though the tables are created properly and I can see them in PhpMyAdmin, I keep getting the following error in console:
Error: exam_question is not associated to exam!
exam.js
...
const ExamQuestion = require('./exam-question');
...
const Exam = sequelizeInstance.define("exam", {
name: { type: Sequelize.STRING },
date: { type: Sequelize.DATE }
});
// Build the model relations
Exam.hasMany(ExamQuestion, { as: "Questions" });
exam-question.js
const ExamQuestion = Sequelize.db.define("exam_question", {
correct_answer: {
type: Sequelize.STRING
},
text: {
type: Sequelize.STRING
}
});
module.exports = ExamQuestion;
To solve the error, I tried:
ExamQuestion.belongsTo(Exam);
But that doesn't change anything.
The query is:
Exam.findAll({
include: [ExamQuestion]
})
How to fix this problem and get the Exam objects including their questions?
TL;DR
For some very non-intuitive reason this seems to be happening because of the as property. To fix the problem, simply remove the as property:
Exam.hasMany(ExamQuestion);
Fixing the methods
By default, after removing the as property, Sequelize will automagically add the following methods: getExam_questions, addExam_question and so on.
They look quite bad: camel and snake cases mixed up together.
To solve that, we can easily define the singular and plural names in the ExamQuestion model options (the third argument):
const ExamQuestion = Sequelize.db.define("exam_question", {
correct_answer: {
type: Sequelize.STRING
},
text: {
type: Sequelize.STRING
}
}, {
name: {
singular: "question",
plural: "questions"
}
});
This will dictate Sequelize to create methods such as getQuestions and addQuestion instead of getExam_questions and addExam_question.
I am currently using StrongLoop as my API backend server and Mongodb as data storage engine.
Let's say there is a collection called article. It has two fields title, and content. And there are two frontend pages to display a list of articles and view a single article.
Obviously the data list page only need title field and the view page need both. Currently the GET method of StrongLoop API return all fields including content. It cost extra traffic. Is there any way that can just return specific field?
Mongodb support projection in find() method for this. How can I do the same thing by StrongLoop?
Have you taken a look at the filters offered. http://docs.strongloop.com/display/LB/Querying+models
Query for NodeAPI:
server.models.Student.findOne({where: {RFID: id},fields: {id: true,schoolId: true,classId: true}}, function (err, data) {
if (err)
callback(err);
else {
callback();
}
})
Query for RestAPI :
$http.get('http://localhost:3000/api/services?filter[fields][id]=true&filter[fields][make]=true&filter[fields][model]=true')
.then(function (response) {
}, function (error) {
});
You can use fields projections,
Sample Record:
{ name: 'Something', title: 'mr', description: 'some desc', patient: { name: 'Asvf', age: 20, address: { street: 1 }}}
First Level Projection:
model.find({ fields: { name: 1, description: 1, title: 0 } })
and I think Strong loop is not yet supporting for second-level object filter, does anyone know how to filter second-level object properties or is yet to implement?.
Second Level Projection: (Need help here)
Ex: 2
model.find({ fields: { name: 1, 'patient.name': 1, 'patient.age': 1, 'patient.address': 0 } })
// Which results { name } only