Advantages<\/h2>\n\n\n\n\n- We can run migration whenever we need.<\/li>\n\n\n\n
- Reduce error generation on production.<\/li>\n\n\n\n
- We can generate migration files from entity changes directly. We don\u2019t need to write migration files.<\/li>\n\n\n\n
- This is particularly useful when working in teams or deploying updates to production systems without disrupting existing data.<\/li>\n\n\n\n
- Each migration file represents a specific set of changes, making it easier to track and manage schema modifications over time.<\/li>\n<\/ul>\n\n\n\n
Disadvantage<\/h2>\n\n\n\n\n- We need to generate migration files for every changes in our entity. After that we need to run it to alter database.<\/li>\n\n\n\n
- If you’re new to migrations or TypeORM, there may be a learning curve involved in understanding the concepts and best practices associated with migrations. This can slow down initial development and require additional effort to grasp the migration workflow.<\/li>\n\n\n\n
- When performing database schema changes, there is always a risk of data loss if not handled carefully. Modifying or deleting columns, tables, or relationships in migrations without proper backup strategies or safeguards can lead to unintentional data loss<\/li>\n<\/ul>\n\n\n\n<\/div>\n\n\n\n
![\"NodeJS](\"https:\/\/www.oneclickitsolution.com\/blog\/wp-content\/uploads\/2022\/02\/NodeJS-CTA-1.png\")
<\/a><\/figure>\n\n\n\nExample<\/h2>\n\n\n\n
Suppose you have an entity named Student something like this:<\/p>\n\n\n\n
import { BaseEntity, Column,Entity, PrimaryGeneratedColumn} from 'typeorm';\n \n@Entity('students')\nexport class Students extends BaseEntity {\n @PrimaryGeneratedColumn()\n id: string;\n \n @Column()\n name: string;\n \n @Column()\n marks: number;\n\n}\n<\/code><\/pre>\n\n\n\nNow you need to alter \u201cname<\/strong>\u201d column with \u201cstudent_name<\/strong>\u201d then you need to create a migration file with the below SQL query<\/p>\n\n\n\nALTER TABLE \"students\" ALTER COLUMN \"name\" RENAME TO \"student_name\";<\/code><\/pre>\n\n\n\nTypeORM provides such functionality that you can store such queries and execute them to alter your database. This functionality is migrations<\/a><\/strong>.<\/p>\n\n\n\nHow to Create New Migrations?<\/h2>\n\n\n\n
Before creating migrations you need to set up your TypeORM config file something like:<\/p>\n\n\n\n
{\n \"type\": \"postgres\",\n \"host\": \"postgres\",\n \"port\": 5432,\n \"username\": \"postgres\",\n \"password\": \"postgres\",\n \"database\": \"elite_opinio\",\n \"entities\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/@config\/..\/**\/entities\/*.entity.{js,ts}\"\n ],\n \"synchronize\": false,\n \"migrations\": [\n \"src\/migrations\/*.ts\"\n ],\n \"migrationsTableName\": \"migrations_TypeORM\",\n \"cli\": {\n \"migrationsDir\": \"src\/migrations\"\n },\n \"seeds\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.seeder.{js,ts}\"\n ],\n \"factories\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.factory.{js,ts}\"\n ]\n}\n<\/code><\/pre>\n\n\n\nFirst of all, you need to close auto sync by setting “synchronize”: false<\/strong><\/p>\n\n\n\nThen you need to specify migration files path in “cli”: {“migrationsDir”: “src\/migrations”}<\/strong>, where all your migration files will generate.<\/p>\n\n\n\nWhile running migrations it will take files from “migrations” : [“src\/migrations\/*.ts”] <\/strong>path.<\/p>\n\n\n\nAlso, we need to add a script for TypeORM in package.json<\/strong> file like:<\/p>\n\n\n\n\"TypeORM\": \"ts-node .\/node_modules\/TypeORM\/cli.js -f .\/ormconfig.json\"<\/code><\/pre>\n\n\n\nAfter setting the config file you need to create a new migration file with: TypeORM migration:create -n PostRefactoring<\/p>\n\n\n\n
This command will generate a new file in src folder like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n \n public async up(queryRunner: QueryRunner): Promise<void> {}\n \n public async down(queryRunner: QueryRunner): Promise<void> {}\n}\n<\/code><\/pre>\n\n\n\nThis file has contain two methods \u201cup\u201d and \u201cdown\u201d. \u201cup\u201d is where you need to write your new SQL changes and \u201cdown\u201d is used to revert those changes.<\/p>\n\n\n\n
Now to alter our column we need to write query something like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n public async up(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" ADD \"status\" boolean NOT NULL DEFAULT false`);\n }\n\n public async down(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" DROP COLUMN \"status\"`);\n }\n}<\/code><\/pre>\n\n\n\nRun Migration<\/h2>\n\n\n\n
To run all migrations we need to execute the command:<\/p>\n\n\n\n
npm run TypeORM migration:run<\/code><\/pre>\n\n\n\nIt will execute the file and alter the column of the student’s table.<\/p>\n\n\n\n
Now, if we follow this process then we need to write queries for every single change. And execute migrations every time. But TypeORM provides functionality to generate migration automatically from entity changes.<\/p>\n\n\n\n
For doing that you just need to run the below command:<\/p>\n\n\n\n
npm run TypeORM migration:generate -- -n MigrationName<\/code><\/pre>\n\n\n\nThis command will generate all new changes in entities that are not in the database. So you can generate files and make changes in the database by running migrations.<\/p>\n\n\n\n![\"NodeJS](\"https:\/\/www.oneclickitsolution.com\/blog\/wp-content\/uploads\/2022\/02\/NodeJS-CTA-2-1.png\")
<\/a><\/figure>\n\n\n\nConclusion<\/h2>\n\n\n\n
Migrations are an essential part of managing database schemas in NestJS applications using TypeORM. They offer a structured approach to handle changes, ensuring data integrity and preventing disruptions in production environments. By utilizing migrations, developers can maintain control over their database structure while minimizing risks associated with direct modifications. <\/p>\n\n\n\n
This practice not only streamlines collaboration in team settings but also safeguards against potential data loss. As you continue to build and scale your applications, incorporating a robust migration strategy will be key to maintaining a reliable and efficient database system.<\/p>\n\n\n\n
Disadvantage<\/h2>\n\n\n\n\n- We need to generate migration files for every changes in our entity. After that we need to run it to alter database.<\/li>\n\n\n\n
- If you’re new to migrations or TypeORM, there may be a learning curve involved in understanding the concepts and best practices associated with migrations. This can slow down initial development and require additional effort to grasp the migration workflow.<\/li>\n\n\n\n
- When performing database schema changes, there is always a risk of data loss if not handled carefully. Modifying or deleting columns, tables, or relationships in migrations without proper backup strategies or safeguards can lead to unintentional data loss<\/li>\n<\/ul>\n\n\n\n<\/div>\n\n\n\n
<\/a><\/figure>\n\n\n\nExample<\/h2>\n\n\n\n
Suppose you have an entity named Student something like this:<\/p>\n\n\n\n
import { BaseEntity, Column,Entity, PrimaryGeneratedColumn} from 'typeorm';\n \n@Entity('students')\nexport class Students extends BaseEntity {\n @PrimaryGeneratedColumn()\n id: string;\n \n @Column()\n name: string;\n \n @Column()\n marks: number;\n\n}\n<\/code><\/pre>\n\n\n\nNow you need to alter \u201cname<\/strong>\u201d column with \u201cstudent_name<\/strong>\u201d then you need to create a migration file with the below SQL query<\/p>\n\n\n\nALTER TABLE \"students\" ALTER COLUMN \"name\" RENAME TO \"student_name\";<\/code><\/pre>\n\n\n\nTypeORM provides such functionality that you can store such queries and execute them to alter your database. This functionality is migrations<\/a><\/strong>.<\/p>\n\n\n\nHow to Create New Migrations?<\/h2>\n\n\n\n
Before creating migrations you need to set up your TypeORM config file something like:<\/p>\n\n\n\n
{\n \"type\": \"postgres\",\n \"host\": \"postgres\",\n \"port\": 5432,\n \"username\": \"postgres\",\n \"password\": \"postgres\",\n \"database\": \"elite_opinio\",\n \"entities\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/@config\/..\/**\/entities\/*.entity.{js,ts}\"\n ],\n \"synchronize\": false,\n \"migrations\": [\n \"src\/migrations\/*.ts\"\n ],\n \"migrationsTableName\": \"migrations_TypeORM\",\n \"cli\": {\n \"migrationsDir\": \"src\/migrations\"\n },\n \"seeds\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.seeder.{js,ts}\"\n ],\n \"factories\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.factory.{js,ts}\"\n ]\n}\n<\/code><\/pre>\n\n\n\nFirst of all, you need to close auto sync by setting “synchronize”: false<\/strong><\/p>\n\n\n\nThen you need to specify migration files path in “cli”: {“migrationsDir”: “src\/migrations”}<\/strong>, where all your migration files will generate.<\/p>\n\n\n\nWhile running migrations it will take files from “migrations” : [“src\/migrations\/*.ts”] <\/strong>path.<\/p>\n\n\n\nAlso, we need to add a script for TypeORM in package.json<\/strong> file like:<\/p>\n\n\n\n\"TypeORM\": \"ts-node .\/node_modules\/TypeORM\/cli.js -f .\/ormconfig.json\"<\/code><\/pre>\n\n\n\nAfter setting the config file you need to create a new migration file with: TypeORM migration:create -n PostRefactoring<\/p>\n\n\n\n
This command will generate a new file in src folder like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n \n public async up(queryRunner: QueryRunner): Promise<void> {}\n \n public async down(queryRunner: QueryRunner): Promise<void> {}\n}\n<\/code><\/pre>\n\n\n\nThis file has contain two methods \u201cup\u201d and \u201cdown\u201d. \u201cup\u201d is where you need to write your new SQL changes and \u201cdown\u201d is used to revert those changes.<\/p>\n\n\n\n
Now to alter our column we need to write query something like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n public async up(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" ADD \"status\" boolean NOT NULL DEFAULT false`);\n }\n\n public async down(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" DROP COLUMN \"status\"`);\n }\n}<\/code><\/pre>\n\n\n\nRun Migration<\/h2>\n\n\n\n
To run all migrations we need to execute the command:<\/p>\n\n\n\n
npm run TypeORM migration:run<\/code><\/pre>\n\n\n\nIt will execute the file and alter the column of the student’s table.<\/p>\n\n\n\n
Now, if we follow this process then we need to write queries for every single change. And execute migrations every time. But TypeORM provides functionality to generate migration automatically from entity changes.<\/p>\n\n\n\n
For doing that you just need to run the below command:<\/p>\n\n\n\n
npm run TypeORM migration:generate -- -n MigrationName<\/code><\/pre>\n\n\n\nThis command will generate all new changes in entities that are not in the database. So you can generate files and make changes in the database by running migrations.<\/p>\n\n\n\n<\/a><\/figure>\n\n\n\nConclusion<\/h2>\n\n\n\n
Migrations are an essential part of managing database schemas in NestJS applications using TypeORM. They offer a structured approach to handle changes, ensuring data integrity and preventing disruptions in production environments. By utilizing migrations, developers can maintain control over their database structure while minimizing risks associated with direct modifications. <\/p>\n\n\n\n
This practice not only streamlines collaboration in team settings but also safeguards against potential data loss. As you continue to build and scale your applications, incorporating a robust migration strategy will be key to maintaining a reliable and efficient database system.<\/p>\n\n\n\n
<\/a><\/figure>\n\n\n\nExample<\/h2>\n\n\n\n
Suppose you have an entity named Student something like this:<\/p>\n\n\n\n
import { BaseEntity, Column,Entity, PrimaryGeneratedColumn} from 'typeorm';\n \n@Entity('students')\nexport class Students extends BaseEntity {\n @PrimaryGeneratedColumn()\n id: string;\n \n @Column()\n name: string;\n \n @Column()\n marks: number;\n\n}\n<\/code><\/pre>\n\n\n\nNow you need to alter \u201cname<\/strong>\u201d column with \u201cstudent_name<\/strong>\u201d then you need to create a migration file with the below SQL query<\/p>\n\n\n\nALTER TABLE \"students\" ALTER COLUMN \"name\" RENAME TO \"student_name\";<\/code><\/pre>\n\n\n\nTypeORM provides such functionality that you can store such queries and execute them to alter your database. This functionality is migrations<\/a><\/strong>.<\/p>\n\n\n\nHow to Create New Migrations?<\/h2>\n\n\n\n
Before creating migrations you need to set up your TypeORM config file something like:<\/p>\n\n\n\n
{\n \"type\": \"postgres\",\n \"host\": \"postgres\",\n \"port\": 5432,\n \"username\": \"postgres\",\n \"password\": \"postgres\",\n \"database\": \"elite_opinio\",\n \"entities\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/@config\/..\/**\/entities\/*.entity.{js,ts}\"\n ],\n \"synchronize\": false,\n \"migrations\": [\n \"src\/migrations\/*.ts\"\n ],\n \"migrationsTableName\": \"migrations_TypeORM\",\n \"cli\": {\n \"migrationsDir\": \"src\/migrations\"\n },\n \"seeds\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.seeder.{js,ts}\"\n ],\n \"factories\": [\n \"\/usr\/src\/eliteopinio\/backend\/dist\/**\/entities\/*.factory.{js,ts}\"\n ]\n}\n<\/code><\/pre>\n\n\n\nFirst of all, you need to close auto sync by setting “synchronize”: false<\/strong><\/p>\n\n\n\nThen you need to specify migration files path in “cli”: {“migrationsDir”: “src\/migrations”}<\/strong>, where all your migration files will generate.<\/p>\n\n\n\nWhile running migrations it will take files from “migrations” : [“src\/migrations\/*.ts”] <\/strong>path.<\/p>\n\n\n\nAlso, we need to add a script for TypeORM in package.json<\/strong> file like:<\/p>\n\n\n\n\"TypeORM\": \"ts-node .\/node_modules\/TypeORM\/cli.js -f .\/ormconfig.json\"<\/code><\/pre>\n\n\n\nAfter setting the config file you need to create a new migration file with: TypeORM migration:create -n PostRefactoring<\/p>\n\n\n\n
This command will generate a new file in src folder like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n \n public async up(queryRunner: QueryRunner): Promise<void> {}\n \n public async down(queryRunner: QueryRunner): Promise<void> {}\n}\n<\/code><\/pre>\n\n\n\nThis file has contain two methods \u201cup\u201d and \u201cdown\u201d. \u201cup\u201d is where you need to write your new SQL changes and \u201cdown\u201d is used to revert those changes.<\/p>\n\n\n\n
Now to alter our column we need to write query something like:<\/p>\n\n\n\n
import {MigrationInterface, QueryRunner} from \"TypeORM\";\n \nexport class Student12345 implements MigrationInterface {\n public async up(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" ADD \"status\" boolean NOT NULL DEFAULT false`);\n }\n\n public async down(queryRunner: QueryRunner): Promise<void> {\n await queryRunner.query(`ALTER TABLE \"students\" DROP COLUMN \"status\"`);\n }\n}<\/code><\/pre>\n\n\n\nRun Migration<\/h2>\n\n\n\n
To run all migrations we need to execute the command:<\/p>\n\n\n\n
npm run TypeORM migration:run<\/code><\/pre>\n\n\n\nIt will execute the file and alter the column of the student’s table.<\/p>\n\n\n\n
Now, if we follow this process then we need to write queries for every single change. And execute migrations every time. But TypeORM provides functionality to generate migration automatically from entity changes.<\/p>\n\n\n\n
For doing that you just need to run the below command:<\/p>\n\n\n\n
npm run TypeORM migration:generate -- -n MigrationName<\/code><\/pre>\n\n\n\nThis command will generate all new changes in entities that are not in the database. So you can generate files and make changes in the database by running migrations.<\/p>\n\n\n\n<\/a><\/figure>\n\n\n\nConclusion<\/h2>\n\n\n\n
Migrations are an essential part of managing database schemas in NestJS applications using TypeORM. They offer a structured approach to handle changes, ensuring data integrity and preventing disruptions in production environments. By utilizing migrations, developers can maintain control over their database structure while minimizing risks associated with direct modifications. <\/p>\n\n\n\n
This practice not only streamlines collaboration in team settings but also safeguards against potential data loss. As you continue to build and scale your applications, incorporating a robust migration strategy will be key to maintaining a reliable and efficient database system.<\/p>\n\n\n\n