Entity Generator

To generate entities from existing database schema, you can use the EntityGenerator helper. It lives in its own package called @mikro-orm/entity-generator:

npm

npm install @mikro-orm/entity-generator

Yarn

yarn add @mikro-orm/entity-generator

pnpm

pnpm add @mikro-orm/entity-generator

The version needs to be aligned with the @mikro-orm/core package and the database driver package.

To use it, you need to register the EntityGenerator extension in your ORM config:

import { defineConfig } from '@mikro-orm/postgresql';
import { EntityGenerator } from '@mikro-orm/entity-generator';

export default defineConfig({
  dbName: 'test',
  extensions: [EntityGenerator],
});

Then you can use it either via CLI:

To work with the CLI, first install @mikro-orm/cli package locally. The version needs to be aligned with the @mikro-orm/core package.

npx mikro-orm generate-entities --dump  # Dumps all generated entities
npx mikro-orm generate-entities --save --path=./my-entities  # Saves entities into given directory

Or you can create simple script where you initialize MikroORM like this:

./generate-entities.ts

import { MikroORM } from '@mikro-orm/core';
import { EntityGenerator } from '@mikro-orm/entity-generator';

(async () => {
  const orm = await MikroORM.init({
    discovery: {
      // we need to disable validation for no entities
      warnWhenNoEntities: false,
    },
    extensions: [EntityGenerator],
    dbName: 'your-db-name',
    // ...
  });
  const dump = await orm.entityGenerator.generate({
    save: true,
    path: process.cwd() + '/my-entities',
  });
  console.log(dump);
  await orm.close(true);
})();

Then run this script via ts-node (or compile it to plain JS and use node):

$ ts-node generate-entities

Advanced configuration

The behaviour of the entity generator can be adjusted either via entityGenerator section in the ORM config, or with the GenerateOptions object (parameter of the generate method), which takes precedence over the global configuration.

Available options:

Option	Description
schema: string	The target schema to generate entities for. Defaults to what the main config would use.
takeTables: (string | RegExp)[]	Consider some database tables. Accepts array of table names and RegExps. If there is a foreign key reference to a non-taken table, the generated code will be as if that foreign key did not exist.
skipTables: (string | RegExp)[]	Ignore some database tables. Accepts array of table names and RegExps. If there is a foreign key reference to a skipped table, the generated code will be as if that foreign key did not exist.
skipColumns	Ignore some database tables columns. Accepts an object, where keys are table names with schema prefix if available, values are arrays of column names and RegExps. If a skipped column is the target of a foreign key reference, the generated code will look as if that foreign key did not exist.
save: boolean	Whether to save the generated entities as files.
path: string	Folder to save the generated entities in, if saving is enabled. Defaults to a folder called generated-entities inside the baseDir of the main config.
fileName: (className: string) => string	Callback to override the entity file name (without extension, relative to the path). Defaults to the entity name. Note that this callback is also called whenever onImport returns undefined.
onImport: ImportsResolver	Callback that is called when importing entities, custom types or extra imports, allowing override of import resolution. Receives (in this order) the identifier requested, folder of requesting file (relative to the output folder; "." when at that folder itself), expected extension for the import, and the current entity file name. When esmImport is true, the extension would be .js, or else it would be an empty string. The return value is an object with properties "path" and "name" that together describe how to import the requested identifier. The property "path" must contain the full path to import, and the property "name" must contain the name to import from that path, with the input identifier being an alias from that name. When "name" matches the input class name, no alias is created. When "name" is "default", a default import is made. When both "path" and "name" are empty, no import is created in the output (useful for runtimeType values that are globals). When "name" is empty, but "path" is not, a namespace import is made. When "path" is empty but "name" is not, a side effects import is made with "name" as the path to import. The callback may also return undefined, in which case, the fileName callback will be used as a fallback. It is recommended to do so for entities.
extraImports: (baseDir: string, fileName: string) => string[] | undefined	Callback to define additional names to be imported at the given file, if not already imported there. This is intended to be used in combination with onInitialMetadata/onProcessedMetadata, where they add custom functions (e.g. serializer, onCreate, onUpdate, etc.) with sources that may need those extra imports. The entity generator is otherwise blind about those identifiers.
bidirectionalRelations: boolean	By default, the EntityGenerator generates only owning sides of relations (e.g. M:1). If set to true, generates also the inverse sides for them
identifiedReferences: boolean	If set to true, generate M:1 and 1:1 relations as wrapped references. Also wraps any lazy properties.
entitySchema: boolean	By default, generate entities using decorators. If true, generate the entities using EntitySchema instead.
esmImport: boolean	By default, import statements for entities without extensions are used. If set to true, uses ESM style import for imported entities, i.e. adds a .js suffix as extension. Also, when not using wrapped references, Rel<> is added around all M:1 and 1:1 relations, to avoid the Cannot access 'X' before initialization class of errors.
scalarTypeInDecorator: boolean	If true, include the type option in scalar property decorators. This information is discovered at runtime, but the process of discovery can be skipped by including this option in the decorator. If using EntitySchema, this type information is always included.
scalarPropertiesForRelations: 'never' | 'always' | 'smart'	'never' (default) - Do not generate any scalar properties for columns covered by foreign key relations. This effectively forces the application to always provide the entire relation, or (if all columns in the relation are nullable) omit the entire relation. 'always' - Generate all scalar properties for all columns covered by foreign key relations. This enables the application to deal with code that disables foreign key checks. 'smart' - Only generate scalar properties for foreign key relations, where doing so is necessary to enable the management of rows where a composite foreign key is not enforced due to some columns being set to NULL. This enables the application to deal with all rows that could possibly be part of a table, even when foreign key checks are always enabled.
onlyPurePivotTables: boolean	By default, M:N relations are allowed to use pivot tables containing additional columns. If set to true, M:N relations will not be generated for such pivot tables.
outputPurePivotTables: boolean	By default, pivot tables that don't contain additional properties are not included in the output, unless they are the target of a foreign key relation. If you prefer to be consistent with your M:N relations, or plan to do some extensions that the generator will be blind towards, you can set this option to true to output all pivot entities, and reference them with the pivotEntity option, regardless of whether those pivot entities have additional columns or not.
readOnlyPivotTables: boolean	By default, M:N relations are only generated if the collection would be writable, i.e. any additional columns need to be optional and have non-unique default values. If set to true, also generate M:N relations even if the collection would be read only (meaning the only way to write to it is by using the pivot entity directly). Such collections will include the persist: false option. This setting is effectively meaningless if onlyPurePivotTables is set to true.
customBaseEntityName: string	By default, entity classes do not extend a base class. If this option is set, a class with this name will be created, if it doesn't exist already, and any entity that does not inherit from another will be made to use this one. The class itself will also be set to contain a [Config] symbol with the currently running configuration.
useCoreBaseEntity: boolean	By default, entity classes do not extend a base class. If this option is set to true, entity classes that do not extend another will be set to use the BaseEntity class in @mikro-orm/core. When combined with the customBaseEntityName option, effectively, only the generated base class will use the core's BaseEntity class.
coreImportsPrefix: string	By default, imports from MikroORM's core are imported without aliases. This may cause problems with the generated code if you have tables or custom types that share the same names (e.g. a table called "entity"). If this option is specified, all core imports will be imported with an alias that starts with this prefix.
onInitialMetadata: MetadataProcessor	A function can be provided to do processing of the initially collected metadata collection. Triggered after checking for tables and columns affected by skipping, but before anything else, including base class generation, ManyToMany relation detection, wrapping references and bi-directional relation detections. This hook is the appropriate place to add virtual and embeddable entities, any owning sides of OneToOne or ManyToOne references and wrapped lazy references. The generator can then figure out the inverse side and/or if any ManyToMany relations are affected. The function may return a promise, in which case, the promise will be awaited before moving on.
onProcessedMetadata: MetadataProcessor	A function can be provided to do processing of the final metadata collection. Triggered after base class generation, ManyToMany relation detection, wrapping references and bi-directional relation detection, just before outputting the metadata into files. This is the appropriate place for changes that need to be universally applied, including to ManyToMany and inverse side relation properties, or to opt out of specific wrapped references and base classes. The function may return a promise, in which case, the promise will be awaited before moving on.

Example configuration:

const dump = await orm.entityGenerator.generate({
  entitySchema: true,
  bidirectionalRelations: true,
  identifiedReferences: true,
  esmImport: true,
  save: true,
  path: process.cwd() + '/my-entities',
  skipTables: ['book', 'author'],
  skipColumns: {
    'public.user': ['email', 'middle_name'],
  },
});

Processing of generated metadata

There are several features that are impossible to infer from the database schema alone.

The configuration settings onInitialMetadata and onProcessedMetadata can be used to add that information to the generated metadata, before the metadata is ultimately saved as a file. Note that this is different from the onMetadata hook in the configuration. The onMetadata hook does not affect the entity files, but those in the generator options do.

Some of the things that are suitable for these hooks include

• Adding the hidden flag on certain columns and relations.
• Adding serialization groups on certain columns and relations.
• Adding the lazy flag on certain columns.
• Adding the eager flag on certain relations.
• Adding the mapToPk flag on certain relations.
• Adding the orphanRemoval flag on certain inverse relations.
• Adding the cascade option on certain relations.
• Tweaking the type and/or runtimeType of scalar fields to custom ones that perform extra (application level) validation.
• Adding Single Table Inheritance definitions.
• Adding @Embedded entities and references to them.
• Adding virtual entities.
• Adding properties with formula.

Example: Adding flags

Here's an example that will make any column named "password" (regardless of what table is defined in) be lazy and hidden in its onInitialMetadata and in onProcessedMetadata will make all ManyToMany relations be hidden.

import { ReferenceKind, MikroORM } from '@mikro-orm/core';

const orm = await MikroORM.init({
  // ORM config
});

await orm.entityGenerator.generate({
  onInitialMetadata: (metadata, platform) => {
    metadata.forEach(meta => {
      meta.props.forEach(prop => {
        if (prop.name === 'password') {
          prop.hidden = true;
          prop.lazy = true;
        }
      });
    });
  },
  onProcessedMetadata: (metadata, platform) => {
    metadata.forEach(meta => {
      meta.props.forEach(prop => {
        if (prop.kind === ReferenceKind.MANY_TO_MANY) {
          prop.hidden = true;
        }
      });
    });
  },
});

Example: Adding @Embedded entities

Adding embedded (as well as virtual entities) via the hooks can be somewhat tricky. The metadata objects are internal, and thus fewer checks are in place on them, meaning any errors are likely to be cryptic.

Here's an example that defines a simple embeddable with just two properties and adds a reference to it that is otherwise known to be a JSON column.

import { ReferenceKind, MikroORM, EntityMetadata } from '@mikro-orm/core';

const orm = await MikroORM.init({
  // ORM config
});

await orm.entityGenerator.generate({
  onInitialMetadata: (metadata, platform) => {
    // Create the Embeddable meta data in the script, rather than in a file.
    const embeddableEntityMeta = new EntityMetadata({
      className: 'IdentitiesContainer',
      collection: platform.getConfig().getNamingStrategy().classToTableName('IdentitiesContainer'),
      embeddable: true,
    });
    embeddableEntityMeta.addProperty({
      name: 'github',
      type: 'string',
      runtimeType: 'string',
      nullable: true,
      fieldNames: ['github'],
      columnTypes: ['varchar(255)'],
    });
    embeddableEntityMeta.addProperty({
      name: 'local',
      type: 'integer',
      runtimeType: 'number',
      nullable: true,
      fieldNames: ['local'],
      columnTypes: ['int'],
    });
    metadata.push(embeddableEntityMeta);

    // Add a reference to the embeddable.
    // This works even if the script does not define the embeddable's meta data.
    // This example assumes there exists an "author" table with a JSON column called "identity".
    const identitiesPropOnAuthor = metadata.find(meta => meta.className === 'Author')!.properties.identity;
    identitiesPropOnAuthor.kind = ReferenceKind.EMBEDDED;
    identitiesPropOnAuthor.array = true;
    identitiesPropOnAuthor.object = true;
    identitiesPropOnAuthor.prefix = false;
    identitiesPropOnAuthor.type = 'IdentitiesContainer';
  },
});

An alternative approach that is perhaps less error-prone (at entity generation time; you would still get runtime validation errors if your definition is erroneous) is to define the embedded entities manually in a file that you then copy to the output folder. The generator's metadata hooks only need to add the references to these embedded entities. Such entities will be imported like any other regular entity.

Either way, you would end up with a file similar to

./my-entities/IdentitiesContainer.ts

import { Embeddable, Property } from '@mikro-orm/core';

@Embeddable()
export class IdentitiesContainer {

  @Property()
  github!: string;

  @Property()
  local!: number;

}

and then in the reference, you will end up with something similar to

./my-entities/Author.ts

import { Embedded, Entity } from '@mikro-orm/core';
import { IdentitiesContainer } from './IdentitiesContainer';

@Entity()
export class Author {
    
  // ...

  @Embedded({ entity: () => IdentitiesContainer, array: true, object: true, prefix: false, nullable: true })
  identity?: IdentitiesContainer[];
  
  // ...

}

Example: Defining custom types for scalar properties

The entity generator will try to look for type names (the value of the "type" property in the previous example) by string first, via the platform's getMappedType() method. If the type is found, the output is that string. If the result of this call is MikroORM's UnknownType, the identifier is assumed to be the name of a class extending MikroORM's Type class, and gets imported. See Custom Types for more details on defining such a class. Note that only a reference to the identifier is used (no "new" added), meaning you are always using a "stateless" type implementation.

So, you may register your custom types at the config (see "Adjusting default type mapping" in "Configuration"), in which case, you should define the same type override in both your entity generation script and your runtime configuration. Or you may not do that, and instead use the class names as type identifiers, in which case, you need to ensure the types are importable by the entity files. To achieve this, you may override the fileName, to conditionally adjust the path to where the type is, relative to your output folder. Or alternatively, you may place the type classes inside your output folder.

You may also change the runtimeType option of properties. If necessary, this type will be wrapped up in IType (see "Mapping to objects and type-safety" in "Custom types") where the runtime type is taken from the property's runtimeType option, and the raw type is taken from the runtimeType of the first customTypes, or if that's not defined, the type's runtimeType, or, in the case of unregistered types, from the runtimeType of the type inferred from the first value in columnTypes. Тhe serialized type will be taken from the runtimeType property of the customType option, or fallback to whatever was inferred for the raw type, and if necessary, that type will be included in the IType wrapper as well. If all of these types are the same, the IType wrapper will not be added around runtimeType.

If you modify the runtimeType of a primary key column, and also reference that same relation with mapToPk at the reference, then at the reference, you may need to add the customTypes array with overrides for each primary key column, in their declaration order. That way, the types between the referenced column and the reference will match.

The following example shows some of the more typical uses.

import { ReferenceKind, MikroORM, EntityMetadata, Type, JsonType } from '@mikro-orm/core';

class MetaAsJsonType extends JsonType {
  get runtimeType(): string {
    return 'MetaType';
  }
}


class UrlType extends Type<URL, string> {
  convertToJSValue(value: string, platform: Platform): URL {
    return new URL(value);
  }

  convertToDatabaseValue(value: URL, platform: Platform, context?: TransformContext): string {
    return value.toString();
  }
}

const orm = await MikroORM.init({
  discovery: {
    warnWhenNoEntities: false,
    getMappedType: (type: string, platform: Platform) => {
      switch (type) {
        case 'metaAsJson':
          return Type.getType(MetaAsJsonType);
        case 'url':
          return Type.getType(UrlType);
        default:
          return platform.getDefaultMappedType(type);
      }
    },
  },
  // ORM config
});

await orm.entityGenerator.generate({
  fileName: (name) => {
    switch (name) {
      case 'Email':
      case 'MetaType':
        return `../runtimeTypes/${name}`;
      default:
        return name;
    }
  },
  onImport: (name, basePath, extension) => {
    switch (name) {
      // In this example, EmailType is actually an alias to a class called Email.
      // But unlike our runtimeType of the same name, it is part of a different larger file.
      case 'EmailType':
        return { path: `${basePath}/../types`, name: 'Email' };
      // In this example, our branded types are the default exports
      // in files named after the type, collectively present in one folder above the entities folder.
      // This is similar to what fileName would resolve to, except here we can use default imports.
      case 'BookVersion':
      case 'AuthorVersion':
        return { path: `${basePath}/../brandedTypes/${name}${extension}`, name: 'default' };
      // URL is a node builtin that is also global. Do not import it.
      case 'URL':
        return { path: '', name: '' };
    }
  },
  onInitialMetadata: (metadata, platform) => {
    // Assume there exists a table "author" with VARCHAR(255) column named "email".
    // We want to hydrate the value into an object that can perform further actions on the email.
    const emailPropOnAuthor = metadata.find(meta => meta.className === 'Author')!.properties.email;
    // The "EmailType" is not registered in the config, so it will be imported.
    emailPropOnAuthor.type = 'EmailType';
    // The "Email" doesn't match what is inferred from DB, so it will be wrapped as IType<Email, string>.
    emailPropOnAuthor.runtimeType = 'Email';
    
    // Assume there exists a table "author" with VARCHAR(255) column named "website".
    // We want to hydrate the value into a URL object.
    const websitePropOnAuthor = metadata.find(meta => meta.className === 'Author')!.properties.website;
    // The "url" is registered in the config, so it will be outputted as a string.
    websitePropOnAuthor.type = 'url';
    // The "URL" doesn't match what is inferred from DB, so it will be wrapped as IType<URL, string>.
    websitePropOnAuthor.runtimeType = 'URL';
    
    // Assume there exists a table "book" with JSON column named "meta".
    // Assume there is a check constraint that ensures it will be an object with a certain shape.
    // We want to enforce it being that same shape on TypeScript level.
    const metaPropOnBook = metadata.find(meta => meta.className === 'Book')!.properties.meta;
    // The "metaAsJson" type is registered as a name in the config, mapped to MetaAsJsonType.
    // Therefore, it will be outputted as the string "metaAsJson" (no import).
    metaPropOnBook.type = 'metaAsJson';
    // The runtimeType matches what we have defined in MetaAsJsonType's runtimeType.
    // The generator is able to look it up due to the registration.
    // Because it matches, there will be no IType.
    // This means we force this shape during create, selects, and serialization.
    // The "MetaType" class itself will be imported.
    metaPropOnBook.runtimeType = 'MetaType';
    
    // Assume there's a "book" table with an "INT" column named "version".
    // Assume there's also an "author" table with an "INT" column named "version".
    // On application level, we want to make sure we don't accidentally mix these versions.
    // We shouldn't compare an author version with a book version,
    // or assign a book version to an author version.
    // The actual underlying type and the things we can do with it should remain the same.
    // We don't want to register or import a new type due to the simplicity of the value.
    // We also don't need an IType wrapper, since we're not transforming the data from its raw form
    // during creation or serialization. We're just concerned with updates and comparrisons.
    // Opaque/branded types are the best means to address this.
    // Because we don't want to override the "type", we need to override "customTypes" instead.
    const versionPropOnBook = metadata.find(meta => meta.className === 'Book')!.properties.version;
    versionPropOnBook.runtimeType = 'BookVersion';
    versionPropOnBook.customTypes = [
      new class extends IntegerType {
        get runtimeType(): string {
          return 'BookVersion';
        }
      }
    ];
    const versionPropOnAuthor = metadata.find(meta => meta.className === 'Author')!.properties.version;
    versionPropOnAuthor.runtimeType = 'AuthorVersion';
    versionPropOnAuthor.customTypes = [
      new class extends IntegerType {
        get runtimeType(): string {
          return 'AuthorVersion';
        }
      }
    ];
  }
});

Current limitations

• In MySQL, TINYINT(1) columns will be defined as boolean properties. There is no true BOOLEAN type in MySQL (the keyword is just an alias for TINYINT(1)).
• MongoDB is not supported.