foreign-key-relationship

问题 Hello I'm trying to make an example of persistence of a OneToMany relationship in which I get the following error: Exception Description: Invalid composite primary key specification. The names of the primary key fields or properties in the primary key class [entitys.OrderItemPK] and those of the entity bean class [class entitys.OrderItem] must correspond and their types must be the same. Also, ensure that you have specified ID elements for the corresponding attributes in XML and/or an @Id on

问题 If I have a table with a primary key (AccLinkID) and a foreign key (aspnet_Users UserID), how can I select the object that the foreign key points to using Linq to Entities. User myUser = _myDB.AccLinkSet.Where(user => user.LinkID == linkId).FirstOrDefault().aspnet_Users; did not work... anyone have any ideas? 回答1: Try this: User myUser = _myDB.AccLinkSet.Include("aspnet_Users") .Where(user => user.LinkID == linkId).FirstOrDefault().aspnet_Users; 回答2: Although you can solve this with Include,

问题 I'm using Symfony 2 with Doctrine. I have 4 classes: Country, District, County and Local. District has a foreign key of Country; County has a foreign of District; Local has a foreign key of District. The problem is that when inserting a County (using data fixtures), I get the error SQLSTATE[23000]: Integrity constraint violation: I dumped the SQL to create the tables and constraints and got this: CREATE TABLE Country (id INT AUTO_INCREMENT NOT NULL, name VARCHAR(255) NOT NULL, insertedAt

问题 I ran into the Foreign Key Constraint Failed (code 787) error when I tried to upgrade my database. The only change I did was try to add a 4th entry to my InsertStatus . I looked around and I read that using ON DELETE CASCADE should solve my problem so I tried placing it at all my FK references and tried again but still the same problem. Logcat points to my onUpgrade and all the DROP TABLES in it ( i tried removing it one at a time to see which ones were bad and apparently all of them were ).

问题 I'd like to find all referencing tables in my db that have a foreign key that points to a specific referenced table. Is there a query that I can run to do this? Not sure if the question is confusing. Let me know if it is and I can try to explain it in more detail. 回答1: The following query or Modification tehreof will do - in Sql server You can also supply catalog and schema info select tab1.TABLE_NAME from INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS as ref inner join INFORMATION_SCHEMA.TABLE

问题 Let's suppose that we have this situation: Tables in database: Country (id, country_name), Person (id, login), CountryManager (id_country, id_person), CountryStakeholder (id_country, id_person) If we had to create the model from the database, using Entity Framework Database-First, in VS we'd have a class like this: class Country { int id; string country_name; virtual ICollection<Person> Person1; // Navigation Properties virtual ICollection<Person> Person2; // ---------||---------- } I've

问题 I want to use trigger to make foreign key in MySql. I have the following tables: 1) 'content' table: teacher_id varchar(20) sub_id varchar(20) path varchar(100) file_name varchar(100) 2) 'teacher' table: teacher_id varchar(20) teacher_name varchar(45) and I am using the following code for trigger(delimiter //): CREATE TRIGGER fk_content_teacher_temp BEFORE INSERT ON `content` FOR EACH ROW BEGIN DECLARE has_row TINYINT; SET has_row = 0; SELECT 1 INTO has_row FROM `teacher` INNER JOIN `content`

问题 I'm trying to develop an application as Model-First with EF. I tried everything to accomplish a table-splitting pattern and a 1:1 relationship but looks like EF just doesn't let me. Assuming I do use Model-First - is there a way to put a 1:1 relationship without messing with the generated files and EF giving that annoying: Multiplicity is not valid in Role 'Blablalah' in relationship 'Blabalbala'. Because the Dependent Role properties are not the key properties, the upper bound of the

问题 I have information about music albums that I want to organise in RDBMS tables with relations between them. I have the following info for each album: artist, album name, year, label, genre, style, rating. So far I think to make 4 tables - artists, albums (name, year, label, rating), genre1 and genre2 (each genre with its styles). On the diagram it looks as follows: But don't know yet how can I establish a connection between albums and the other three tables? I.e., when I will run a query

问题 I have a set of tables that look like: workflows = Table('workflows', Base.metadata, Column('id', Integer, primary_key=True), ) actions = Table('actions', Base.metadata, Column('name', String, primary_key=True), Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True), ) action_dependencies = Table('action_dependencies', Base.metadata, Column('workflow_id', Integer, ForeignKey(workflows.c.id), primary_key=True), Column('parent_action', String, ForeignKey(actions.c.name),