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Series on sharing simple insights I've learned. While some may seem basic, there are always others who, like me, may not be aware. Join me in discovering and sharing small, valuable lessons.
Problem Statement While working on a Nestjs project, I encountered a weird problem related to the database column. I was trying to insert a record into a MySQL table using TypeORM. The error I was experiencing stated that a specific column “cannot be...
Motivation Recently, I tried to learn some low-level system programming stuff. I am a Mac user, and I thought that everything that works on Linux should also work on Mac. After all, Mac is a Unix-based system 😊. I guess we all heard this. Oh boy! I ...
Problem Statement While working on a Nestjs project, I encountered a weird problem related to the database column. I was trying to insert a record into a MySQL table using TypeORM. The error I was experiencing stated that a specific column “cannot be...
Recently, I was exploring design patterns courses on my LinkedIn Learning subscription. I came across a course, Node.js: Design Patterns by Alex Banks. It is a wonderful, easy-to-understand course. I started with the Builder Pattern, and the explanat...
Suppose you are working on a table in a LiveView project. This table has limited static data of not more than one page (you can avoid questions about pagination in the comment section 😊). From a user's point of view, it becomes hard to look into the...
Recently, while working on one of my personal Elixir projects. I came across a scenario where I needed to make some changes to the database schema.The changes mainly revolve around adding and removing indexes due to changes in the business requiremen...
Sequelize offers support for read replication, enabling the use of multiple servers for executing SELECT queries. In this configuration, you designate one or more servers as read replicas, while appointing one server as the primary writer. The primary writer manages all write and update operations, disseminating them to the designated replicas. It's important to note that Sequelize does not handle the actual replication process; this responsibility lies with the database backend, requiring proper setup.
const sequelize = new Sequelize('database', null, null, {
dialect: 'mysql',
port: 3306,
replication: {
read: [
{ host: '8.8.8.8', username: 'read-1-username', password: process.env.READ_DB_1_PW },
{ host: '9.9.9.9', username: 'read-2-username', password: process.env.READ_DB_2_PW }
],
write: { host: '1.1.1.1', username: 'write-username', password: process.env.WRITE_DB_PW }
},
pool: {
max: 20,
idle: 30000
},
})
Recently, I came across a situation where I was creating(writing) data and immediately on the next line was returning the created record along with some association as an API response but the record was returning empty.
const recordIds = await fileService.create(req.files)
const files = await fileService.list({ id: recordIds })
return response(res, {record: files})
The fileService.create function creates record file records in the database and returns an array of ids of the files created. In the next line i.e. the fileService.list function takes the array of IDs, fetches the record, and returns an API response in the last line. Below is the implementation of the list function
async list(ids) {
return await Model.findAll({
where: {
id: ids
},
...associationQuery
})
}
This looks plain and simple but for some reason, the list function didn't return any record. I did a lot of debugging and everything looked fine. Then I came across the property useMaster. The read replication we read about in our introduction takes some time to replicate in the read pool. The write or useMaster: true query uses a write pool to create or fetch data. So, the useMaster: true property fixes the issue of fetching data immediately after creating and it fulfills my requirement. Hence, I added useMaster: true in the above query. So the above list function becomes like this 👇
async list(ids) {
return await Model.findAll({
where: {
id: ids
},
...associationQuery,
useMaster: true // New added line
})
}
The above code fixed the issue of data not being fetched in read replicas. I hope you like this small TIL blog. If you have any questions please comment below. Thanks for reading 😊.