entity-relationship

问题 I have doubts in the following relationship: An equipment consists of one or more products But one product can only be connected to that equipment and not another I came to this relationship, but I don't know if it is correct or I can improve if that way a product can only belong to one piece of equipment and one piece of equipment can have more than one product. 来源： https://stackoverflow.com/questions/62764976/entity-relationship-product-and-equipment

问题 I am facing an issue where the data is getting fechted recursively. I wanted to avoid the child to fetch the parent data. Which is causing a recursive issue. I have mentioned the code below Pojo Structure class Parent { .. @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY) private List<Child> childs; .. } class Child { .. @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "parentId") private Parent parent; .. } Fetching the data like this ` em = EMF.get().createEntityManager(); Query

问题 I am facing an issue where the data is getting fechted recursively. I wanted to avoid the child to fetch the parent data. Which is causing a recursive issue. I have mentioned the code below Pojo Structure class Parent { .. @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY) private List<Child> childs; .. } class Child { .. @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "parentId") private Parent parent; .. } Fetching the data like this ` em = EMF.get().createEntityManager(); Query

问题 I have two entities: @Entity({ name: 'provider' }) export class ProviderEntity extends GenericEntity { @Column() name: string; @Column() description: string; @OneToMany(() => ItemEntity, item => item.provider) items: Promise<ItemEntity[]>; } @Entity({ name: 'item' }) export class ItemEntity extends GenericEntity { @Column() content: string; @ManyToOne(() => ProviderEntity, provider => provider.items) provider: Promise<ProviderEntity>; } Provider object already exist in database and I would

问题 I have two entities: @Entity({ name: 'provider' }) export class ProviderEntity extends GenericEntity { @Column() name: string; @Column() description: string; @OneToMany(() => ItemEntity, item => item.provider) items: Promise<ItemEntity[]>; } @Entity({ name: 'item' }) export class ItemEntity extends GenericEntity { @Column() content: string; @ManyToOne(() => ProviderEntity, provider => provider.items) provider: Promise<ProviderEntity>; } Provider object already exist in database and I would

问题 I have two entities: @Entity({ name: 'provider' }) export class ProviderEntity extends GenericEntity { @Column() name: string; @Column() description: string; @OneToMany(() => ItemEntity, item => item.provider) items: Promise<ItemEntity[]>; } @Entity({ name: 'item' }) export class ItemEntity extends GenericEntity { @Column() content: string; @ManyToOne(() => ProviderEntity, provider => provider.items) provider: Promise<ProviderEntity>; } Provider object already exist in database and I would

问题 Got the following datamodel: class EntityA { Guid Id { get; set; } //Property1 and Property2 will never be the same EntityB Property1 { get; set; } EntityB Property2 { get; set; } } class EntityB { int Id { get; set; } EntityA EntityAProperty { get; set; } } But I can't manage to configure the relation. EntityA references two different EntityB. Please give me some advise on how to configure it. Tried something like (for property1 and property2): e.HasOne(x => x.Property1) .WithOne()

问题 I was wondering when one would represent a relationship between an entity set and a relationship with a ternary relationship? I understand the benefit of aggregation, but why use it if there is no attribute in the relationship between the entity set and the relationship set? For instance, a grad student (with a student # and name) works on a project (with pid, start date, and end date) and each project that a student works on has a supervising professor. Every project must have only one

问题 I am trying to understand solution on one exercise that translates ER model to functional dependencies. As you can see above, we only have relation names and nothing else besides that, and by solution, they somehow come up to conclusion that mother, daughter → father father, daughter → mother mother, son → father father, son → mother And that moreover we can infer additional f dependencies to represent real world more accurately: mother, son → father father, son → mother What I don't

问题 When I create a one-to-one relationship migration, laravel creates a one-to-many relationship. PHP 7.1 & MySQL 5.7 The models are: Persona & User. Persona: public function user() { return $this->hasOne('App\User', 'persona_id', 'id'); } User: public function persona() { return $this->belongsTo('App\Persona', 'persona_id', 'id'); } Migrations: Schema::create('users', function (Blueprint $table) { $table->increments('id'); $table->integer('persona_id')->unsigned(); $table->foreign('persona_id')