typeorm/docs/faq.md

FAQ

• How do I change a column name in the database?
• How can I set value of default some function, for example NOW()?
• How to do validation?
• What does "owner side" in relations mean or why we need to put @JoinColumn and @JoinTable decorators?
• How do I add extra columns into many-to-many (junction) table?
• How to use TypeORM with dependency injection tool?
• How to handle outDir TypeScript compiler option?
• How to use TypeORM with ts-node?

How do I update a database schema?

One of the main responsibility of TypeORM is to keep your database tables in sync with your entities. There are two ways that help you to achieve this:

• Use synchronize: true in your connection options:

  import {createConnection} from "typeorm";
  
  createConnection({
      synchronize: true
  });
  

  This option automatically synces your database tables with the given entities each time you run this code. This option is perfect during development, but in production you may not want this option to be enabled.

• Use command line tools and run schema sync manually in the command line:

  typeorm schema:sync
  

  This command will execute schema synchronization. Note, to make command line tools to work, you must create a ormconfig.json file.

Schema sync is extremely fast. If you are considering to disable synchronize option during development because of performance issues, first check how fast it is.

How do I change a column name in the database?

By default column names are generated from property names. You can simply change it by specifying a name column option:

@Column({ name: "is_active" })
isActive: boolean;

How can I set the default value to some function, for example NOW()?

default column option supports a function. If you are passing a function which returns a string, it will use that string as a default value without escaping it. For example:

@Column({ default: () => "NOW()" })
date: Date;

How to do validation?

Validation is not part of TypeORM because validation is a separate process not really related to what TypeORM does. If you want to use validation use class-validator - it works perfectly with TypeORM.

What does "owner side" in a relations mean or why we need to use @JoinColumn and @JoinTable?

Let's start with one-to-one relation. Let's say we have two entities: User and Photo:

@Entity()
export class User {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @Column()
    name: string;
    
    @OneToOne()
    photo: Photo;
    
}

@Entity()
export class Photo {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @Column()
    url: string;
    
    @OneToOne()
    user: User;
    
}

This example does not have a @JoinColumn which is incorrect. Why? Because to make a real relation we need to create a column in the database. We need to create a column userId in photo or photoId in user. But which column should be created - userId or photoId? TypeORM cannot decide it for you. To make a decision you must use @JoinColumn on one of the sides. If you put @JoinColumn in Photo then a column called userId will be created in the photo table. If you put @JoinColumn in User then a column called photoId will be created in the user table. The side with @JoinColumn will be called "owner side of the relationship". The other side of the relation, without @JoinColumn is called "inverse (non-owner) side of relationship".

Same in a @ManyToMany relation you use @JoinTable to show the owner side of the relation.

In @ManyToOne or @OneToMany relations @JoinColumn is not necessary because both decorators are different and where you put @ManyToOne decorator that table will have relational column.

@JoinColumn and @JoinTable decorators can also be used to specify additional join column / junction table settings, like join column name or junction table name.

How do I add extra columns into many-to-many (junction) table?

Its not possible to add extra columns into the table created by a many-to-many relation. You'll need to create a separate entity and bind it using two many-to-one relations with target entities (effect will be same as creating a many-to-many table), and add extra columns in there.

How to use TypeORM with a dependency injection tool?

In TypeORM you can use service containers. Service containers allow you to inject custom services in some places, like in subscribers or custom naming strategies. Or for example, you can get access to ConnectionManager from any place using a service container.

Here is a example for how you can setup typedi service containers with TypeORM. But note, that you can setup any service container with TypeORM.

import {useContainer, createConnection} from "typeorm";
import {Container} from "typedi";

// its important to setup container before you start to work with TypeORM
useContainer(Container);
createConnection({/* ... */});

How to handle outDir TypeScript compiler option?

When you are using the outDir compiler option don't forget to copy assets and resources your app is using into the output directory. Or make sure to setup correct paths to those assets.

One important thing to know is, that when you remove or move entities, the old entities are left untouched inside the ouput directory. For example you create a Post entity and rename it to Blog. You no longer have Post.ts in your project, however Post.js is left inside the output directory. Now when TypeORM reads entities from your output directory it sees two entities - Post and Blog. This may be a source of bugs. That's why when you remove and move entities with outDir enabled its strongly recommended to remove your output directory and recompile the project again.

How to use TypeORM with ts-node?

You can prevent compiling files each time using ts-node. If you are using ts-node you can specify ts entities inside your connection options:

{
    entities: ["src/entity/*.ts"],
    subscribers: ["src/subscriber/*.ts"]
}

Also, if you are compiling js files into the same folder where your typescript files are, make sure to use the outDir compiler option to prevent this issues.

Also if you want to use the ts-node CLI you can execute TypeORM the following way:

ts-node ./node_modules/bin/typeorm schema:sync