foreign-key-relationship

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` ON content.teacher_id=teacher.teacher_id; IF has_row=0 THEN INSERT error_msg VALUES ('Foreign Key

I have 2 object entities (User and Phone) and they are supposed to have many-to-many relations. User.java //all columns @ManyToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER) @JoinTable(name = "USER_PHONE", joinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "phone_id", referencedColumnName = "id")) private List<Phone> phones; Phone.java //all columns @ManyToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER) @JoinTable(name = "USER_PHONE", joinColumns = @JoinColumn(name = "phone_id", referencedColumnName = "id"),

Evening all I have been working on a small application but kind of stuck at the SQLite foreign key constraint. Basically what i have is one "HostLookuptable" as CREATE TABLE tblHostLookup ( HostID INTEGER PRIMARY KEY AUTOINCREMENT, HostName TEXT); And one "ScanLookuptable" as CREATE TABLE tblScanLookup ( ScanID INTEGER PRIMARY KEY AUTOINCREMENT, ScanDate TEXT); Then there is another table that will have mapping between two tables as "ScanHistorytable" CREATE TABLE tblScanHistory ( ScanHistoryID INTEGER PRIMARY KEY AUTOINCREMENT, HostID INTEGER, FOREIGN KEY(HostID) REFERENCES tblHostLookup

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 multiplicity of the Dependent Role must be *. I already tried to set my FK's as Primary Keys on destination

This is probably a trivial question, but I'm still a little clumsy when it comes to foreign key constraints so I wanted to make sure. Let's say I have a table countries with the fields country_id (PK) and name , and a table cities with the fields city_id (PK), name and country_id (FK). The foreign key cities.country_id has the constraint ON DELETE SET NULL . As I understand it, this means that if a record from countries is deleted, any records in cities that reference that deleted record's country_id will have its country_id field set to NULL. What if, however, cities.country_id has the

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 select name from artists I would like to receive an album with corresponding artist and genre-style. How

I am developing a web based application in Grails. I have come across a situation where I would like to try and suppress GORM from creating a foreign key constraint on a field in a table. I have a domain class which is part of a class hierarchy. The domain class essentially acts as a link to a target domain. The target domain can be of different types and each of the subclasses of this link domain is designed to provide the link for each specific type of linked item. These linked items have certain behaviour in common i.e. implement the same interface but otherwise are different to the point