relationship

JPA Bidirectional relationship - infinite loop / circular reference

由 与世无争的帅哥 提交于 2020-01-03 15:56:24
问题 I have a bidirectional relationship @Entity @Table(name = "facility") public class Facility implements Serializable { @Id @GeneratedValue private Long id; @OneToMany(mappedBy = "facility") private Set<Amenity> amenities; } @Entity @Table(name = "amenity") public class Amenity implements Serializable { @Id @GeneratedValue private Long id; @ManyToOne private Facility facility; } This all works fine and I can see the table is created correctly. I can add data fine through a rest endpoint and but

'Many to two' relationship

由 五迷三道 提交于 2020-01-03 11:39:09
问题 I am wondering about a 'many to two' relationship. The child can be linked to either of two parents, but not both. Is there any way to reinforce this? Also I would like to prevent duplicate entries in the child. A real world example would be phone numbers, users and companies. A company can have many phone numbers, a user can have many phone numbers, but ideally the user shouldn't provide the same phone number as the company as there would be duplicate content in the DB. 回答1: This question

mysql中数据去重和优化

由 老子叫甜甜 提交于 2020-01-03 08:34:19
更改表user_info的主键uid为自增的id后，忘了设置原来主键uid属性为unique，结果导致产生uid重复的记录。为此需要清理后来插入的重复记录。 基本方法可以参考后面的附上的资料，但是由于mysql不支持同时对一个表进行操作，即子查询和要进行的操作不能是同一个表，因此需要通过零时表中转一下。 写在前面：数据量大时，一定要多涉及的关键字段创建索引！！！否则很慢很慢很慢，慢到想死的心都有了 1 单字段重复 生成零时表，其中uid是需要去重的字段 create table tmp_uid as (select uid from user_info group by uid having count(uid)) create table tmp_id as (select min(id) from user_info group by uid having count(uid)) 数据量大时一定要为uid创建索引 create index index_uid on tmp_uid create index index_id on tmp_id 删除多余的重复记录，保留重复项中id最小的 delete from user_info where id not in (select id from tmp_id) and uid in (select uid from tmp_uid

Laravel - Many-to-Many polymorphic relationships

由 ﹥＞﹥吖頭↗ 提交于 2020-01-02 08:48:48
问题 I'm banging my head against a polymorphic relationship definition within Laravel 5.7 Here's the data situation: I have a model for Users, a model for Products and a model for Merchandising I basically want to build a WishList for my user, that can contain both Merchandises and Products, and I want to have a polymorphic relationship there because I will have to add new types of things to sell at a later time. In my (simplified) current data schema, I have users -email -id products -id -name

How to manage relationship between 3 resources in REST API

由 故事扮演 提交于 2020-01-02 04:42:09
问题 I'm creating an API based on REST concept but I'm still a bit confused talking about relating resources. I've a website where people can signup in multiple groups and choose multiple roles. For example let's take people that signup in companies as scenario: Companies Facebook Google Apple Roles Marketing Sales Development Customer support So, when I want to create a user in a new company with certain roles, I would pass something like this into a POST request to /users endpoint { "username" :

ruby on rails - how to make relationship works in route, controller, view ? has_many, belongs_to

由 纵然是瞬间 提交于 2020-01-02 04:38:06
问题 I am struggling to get my relationship in rails to work. I have a User,Gallery,Comment model class Gallery has_many :comments belongs_to :user end class User has_many :comments has_many :galleries end class Comment belongs_to :gallery belongs_to :user end now what should i do in the routes, controller and views to link this all up ? please help me ? its quite confusing finding out the answers. If can, I dont want it to be nested like in the railscast, but i want for each model, eg gallery i

Laravel Eloquent - firstOrCreate() on a relationship

由 痴心易碎 提交于 2020-01-02 03:47:09
问题 When I try the firstOrCreate() on a relationship of another model, it does not work: Client::find($id)->users()->firstOrCreate(array('email' => $email)); This returns an error saying Call to undefined method Illuminate\Database\Query\Builder::firstOrCreate() Running this directly on the model User will work though. 回答1: This won't work, you have to do it manually/directly using User model because users() should return a collection object This is correct, the users() function does not return a

unique pair in a “friendship” database

由 蹲街弑〆低调 提交于 2020-01-02 03:28:05
问题 I'm posting this question which is somewhat a summary of my other question. I have two databases : 1) db_users. 2) db_friends. I stress that they're stored in separate databases on different servers and therefore no foreign keys can be used. In 'db_friends' I have the table 'tbl_friends' which has the following columns: - id_user - id_friend Now how do I make sure that each pair is unique at this table ('tbl_friends')? I'd like to enfore that at the table level, and not through a query. For

How do I get all children from a given parent node?

由 筅森魡賤 提交于 2020-01-01 12:07:10
问题 I have a list of parent/child IDs and would like to get all child IDs for a given parent ID. There are no null parents (the top level IDs don't appear as child IDs). Currently the parent/child IDs are recorded as a KeyValuePair in a list, however this could be easily changed to another data structure if that would be better: List<KeyValuePair<int, int>> groups = new List<KeyValuePair<int, int>>(); groups.Add(new KeyValuePair<int,int>(parentID, childID)); For example, here are sample parent

Sqlalchemy: secondary relationship update

由 十年热恋 提交于 2019-12-31 14:32:51
问题 I have two tables, say A and B. Both have a primary key id. They have a many-to-many relationship, SEC. SEC = Table('sec', Base.metadata, Column('a_id', Integer, ForeignKey('A.id'), primary_key=True, nullable=False), Column('b_id', Integer, ForeignKey('B.id'), primary_key=True, nullable=False) ) class A(): ... id = Column(Integer, primary_key=True) ... rels = relationship(B, secondary=SEC) class B(): ... id = Column(Integer, primary_key=True) ... Let's consider this piece of code. a = A() b1
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