foreign-keys

问题 i'm having trouble configuring a foreign key relationship in my Entity Framework fluent Api: Here is the head of the report: public class Testata { public Testata() { Details = new List<Dettaglio>(); } public virtual int IDTEST { get; set; } public virtual string Value { get; set; } public virtual int IDDETAIL { get; set; } public virtual string IDTESTALT { get; set; } public virtual byte[] BLOB { get; set; } public virtual IList<Dettaglio> Details { get; set; } } This is the report's detail

问题 i'm having trouble configuring a foreign key relationship in my Entity Framework fluent Api: Here is the head of the report: public class Testata { public Testata() { Details = new List<Dettaglio>(); } public virtual int IDTEST { get; set; } public virtual string Value { get; set; } public virtual int IDDETAIL { get; set; } public virtual string IDTESTALT { get; set; } public virtual byte[] BLOB { get; set; } public virtual IList<Dettaglio> Details { get; set; } } This is the report's detail

问题 I'm building a small application and setting up foreign key relationships between tables. However I'm confused as to WHY I really need this? What is the advantage - does it assist me when writing my queries that I don't have to perform any joins? Here's an example snippet of my database: +-------------------+ | USERS | +-------------------+ | user_id | | username | | create_date | +-------------------+ +-------------------+ | PROJECTS | +-------------------+ | project_id | | creator | | name

问题 I would like to rename a column in a table that is a foreign key to many tables. Apparently this is only possible if you delete the constraints, as I found out in this link. I dont want to delete all the constratints manually is there a way to delete all the foreign key constraints in the database? I have also tried SET FOREIGN_KEY_CHECKS=0; but I still cant rename the column. 回答1: Executing the following query select * from information_schema.key_column_usage will show you all the

问题 I would like to rename a column in a table that is a foreign key to many tables. Apparently this is only possible if you delete the constraints, as I found out in this link. I dont want to delete all the constratints manually is there a way to delete all the foreign key constraints in the database? I have also tried SET FOREIGN_KEY_CHECKS=0; but I still cant rename the column. 回答1: Executing the following query select * from information_schema.key_column_usage will show you all the

问题 I am creating FOREIGN KEY on Table1(propType) from Table2 with groupName. But i am facing below error. selected columns dont have compatiable type , even it has same type in mysql Table 1 : CREATE TABLE `configuration_master` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `insertTimestamp` datetime DEFAULT NULL, `propName` varchar(255) COLLATE utf8_unicode_ci NOT NULL, `propValue` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL, `propType` varchar(45) COLLATE utf8_unicode_ci DEFAULT NULL,

问题 I have 3 models: Post : id title body Photo : id filepath Comment : id post_id body and corresponding tables in DB. Now, if I want to have comments only for my posts I can simply add following foreign key: ALTER TABLE comment ADD FOREIGN KEY (post_id) REFERENCES post (id) . But I want to have comments for other models (photo, profile, video, etc) and keep all comments in one table. How can I define foreign keys (i definitely need FKs for ORM) in such case? 回答1: You could do this: post: * post

问题 I have 3 tables; teachers table, subjects table and events table. 1.There is one to many relationship between subjects and teachers, that is each teacher can teach only one subject but, many teachers can teach same subjects. 2.There is a many to many relationship between teachers and events. Example of subjects table id(PK) | name ------------------- 1 | php ------------------- 2 | java ------------------- 3 | python ------------------- 4 | c++ -------------------- 5 | c# Example of teachers

问题 I have a PostgreSQL database, 3 tables and my schema as follows --- Parent Table CREATE TABLE IF NOT EXISTS abc.parent( record_id SERIAL PRIMARY KEY, description text NOT NULL ); --- Child Table CREATE TABLE IF NOT EXISTS abc.child ( total_count INT NOT NULL) INHERITS (abc.parent); -- Detail CREATE TABLE abc.detail( detail_id int NOT NULL, detail_description text NOT NULL record_id int NOT NULL, FOREIGN KEY (record_id) REFERENCES abc.parent(record_id) ); Then i insert records in to both

问题 I have a question on creating multiple tuples in multiple tables using Java. Here are my tables. create table department( dept_name varchar(20) primary key, building varchar(15), budget numeric(12,2) ); create table student (ID int, name varchar(20) not null, dept_name varchar(20), tot_cred numeric(10,0), primary key (ID), foreign key (dept_name) references department(dept_name) ); And what I am trying to accomplish is that the java program will prompt the user with "How many tuples would you