Publish to my blog (weekly)

• Using CLI - typeorm

  • To check what sql queries schema:sync is going to run use:
  • typeorm schema:log

• Entity Listeners and Subscribers - typeorm

  • What is a Subscriber

• Transactions - typeorm

  • All operations MUST be executed using the provided transactional entity manager.

• Migrations - typeorm

  • the typescript files need to be compiled before running the commands.
  • ypeORM is able to automatically generate migration files with schema changes you made.
  • Alternatively you can also output your migrations as Javascript files using the o (alias for --outputJs) flag
  • typeorm migration:generate -n PostRefactoring
  • The migration:run and migration:revert commands only work on .js files.
  • To apply multi-line formatting to your generated migration queries, use the p (alias for --pretty) flag.
  • ts-node $(yarn bin typeorm) migration:run
  • ts-node --transpile-only ./node_modules/typeorm/cli.js migration:run

• Many-to-one / one-to-many relations - typeorm

  • await connection.manager.save(photo1);
  • await connection.manager.save(photo2);
  • await connection.manager.save(user);
  • @ManyToOne(() => User, user => user.photos)
  • user.photos = [photo1, photo2];

    12

    await connection.manager.save(user);
  • photo1.user = user;

    8

    await connection.manager.save(photo1);
  • .leftJoinAndSelect("user.photos", "photo")
  • photo2.user = user;

    13

    await connection.manager.save(photo2);
  • Where you set @ManyToOne - its related entity will have "relation id" and foreign key.
  • leftJoinAndSelect("photo.user", "user")
  • don't have to specify relations in the find command as it will ALWAYS be loaded automatically
  • eager loading enabled on a relation
  • use QueryBuilder eager relations are disabled, you have to use leftJoinAndSelect to load the relation.
  • userId | int(11) | FOREIGN KEY

• Many-to-many relations - typeorm

  • A question can have multiple categories, and each category can have multiple questions.
  • Bi-directional relations allow you to join relations from both sides using QueryBuilder:
  • @JoinTable() is required for @ManyToMany relations. You must put @JoinTable on one (owning) side of relation.
  • post.postToCategories
  • @JoinTable must be only on one side of the relation.
  • eager loading enabled on a relation
  • we did not call save or softRemove for category1 and category2, but they will be automatically saved and soft-deleted when the cascade of relation options is set to true like this:
  • you use QueryBuilder eager relations are disabled,
  • ALWAYS be loaded automatically.
  • category.postToCategories
  • @ManyToOne(()
  • leftJoinAndSelect to load the relation.
  • await connection.manager.softRemove(newQuestion);
  • @ManyToOne(()
  • cascade: true
  • public post!: Post;
  • question_categories_category
  • public category!: Category;
  • public postToCategories!: PostToCategory[];
  • @OneToMany(()
  • @OneToMany(()
  • public postToCategories!: PostToCategory[];
  • @JoinTable()

• Entity Inheritance - typeorm

  • Single Table Inheritance

• Entities - typeorm

  • When you'll load data from the database, you will have your object/array/primitive back via JSON.parse

• Eager and Lazy Relations - typeorm

  • Promise<Question[]>;
  • Eager relations only work when you use find* methods. If you use QueryBuilder eager relations are disabled and have to use leftJoinAndSelect to load the relation. Eager relations can only be used on one side of the relationship, using eager: true on both sides of relationship is disallowed.
  • await question.categories;
  • question.categories = Promise.resolve([category1, category2]);
  • n JavaScript and Node.JS you have to use promises if you want to have lazy-loaded relations. This is non-standard technique and considered experimental in TypeORM.
  • Promise<Category[]>;

• [미적분학 (Calculus)] 편미분 (Partial Derivative)이란? : 네이버 블로그

  • 여러 변수에 대한 함수의 편미분이라는 것은 여러 변수들 중 하나에 대해서 미분하고, 나머지는 상수로 취급하는 것을 의미한다.
  • 미분 기하학
  • 벡터 계산
  • z = f(x, y, ...)에 대해서, z를 x에 대해서 편미분
  • 편미분은 일반적으로 본래의 함수에서와 같은 인수를 가지므로
  • y에 대한 미분의 경우에는 반대로 x를 상수치급해서 y에 대해서만 미분을 계산

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