foreign-keys

问题 I trying to create foreign key in MySQL using MySQL workbench. But there is an error $ Executing: ALTER TABLE `project_course`.`attendance` ADD CONSTRAINT `FK_Student` FOREIGN KEY ('idStudent') REFERENCES `project_course`.`student` ('userid') ON DELETE NO ACTION ON UPDATE NO ACTION; Operation failed: There was an error while applying the SQL script to the database. ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right

问题 I have multiple forms on my site that work and save info to my PostgreSQL database. I am trying to create a form to save information for my Set Model: class Set(models.Model): settitle = models.CharField("Title", max_length=50) setdescrip = models.CharField("Description", max_length=50) action = models.ForeignKey(Action) actorder = models.IntegerField("Order number") The Set Form looks like this. I am using ModelChoiceField to pull a list of Action name fields from the Action model, this

问题 I need to drop a deprecated, empty table from my MySQL Database. The table definition is noddy: CREATE TABLE IF NOT EXISTS `Address` ( `Id` int(11) NOT NULL AUTO_INCREMENT, `ContactId` int(11) NOT NULL, PRIMARY KEY (`Id`), KEY `ContactId` (`ContactId`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ; This results in #1217 - Cannot delete or update a parent row: a foreign key constraint fails There was a constraint on ContactId but II've removed it. PHPMyAdmin's export function doesn't

问题 can it make sense for one table to have multiple foreign keys? Suppose I have three tables, Table A , Table B and Table C . If I think of the tables as objects (and they are mapped to objects in my code), then both Tables A and B have a many to one relationship with Table C. I.e. Table/object A and B can each have many instances of C. So the way I designed it is that Table C points to the primary key in both Table A and Table B : in other words, Table C has 2 foreign keys (a_Id, and b_Id).

问题 I have two tables in an existing (MSSQL 2008 R2) database that are related by a link table. The two tables are "Plan" and "Tips". The link table is "PlanTipLinks". Plans can have many tips, and tips can be associated with multiple plans (i.e. it's a many-to-many relationship). In the application, I only care about the "Plan.Tips" relationship. I don't need the Tip.Plans inverse relationship. The foreign key references in the link table cannot be null. I'm using the following fluent API code

问题 Motivation : My EF4.1 DbContext is saving Entities in the wrong order Reason : Lack of navigation properties on my models How I want to fix it : I want to set up foreign key relationships in my DbContext. The catch is that my entity objects have no navigation properties (I'm using it to populate a web service and then firing DTO objects over to my application). The classes below would be an example. In MinorClass, I want to configure my context so that it knows MajorClassID is a foreign key.

问题 I have 2 tables: products and categories . Each category has many products, and a product can belong to many categories. products product_id - int primary auto increment name - unique etc. categories category_id - int primary auto increment name - unique etc. I have a 3rd table for manyTomany relations. products_categories product_id -> foreign key: products.product_id category_id -> foreign key: category.category_id My question is: should I create indexes for product_id and category_id in

问题 I am working on a cookbook website using django and have run into a problem with a foreign key field in my form the problem is that when i create my recipe i need to have a foreign key pointing to the cookbook that created this recipe but I don't want the user creating the recipe to see the original_cookbook field (they shouldn't have to) I believe I need to use a widget (HiddenInput) but am I getting confused with the examples given on other sites. Also my friend mentioned something about

问题 I need somebody help me to figure out the cause of following deadlock. the involved tables are parent/child and child table has indexed FK. parent:PK_FMS_FC_MAIN_FLD_INPUT_LIMIT chile:FMS_FC_REL_FLD_INPUT_LIMIT Deadlock graph: ---------Blocker(s)-------- ---------Waiter(s)--------- Resource Name process session holds waits process session holds waits TX-0019000b-0000b486 22 2755 X 57 492 S TX-00010019-00061e13 57 492 X 22 2755 S session 2755: DID 0001-0016-00000FCE session 492: DID 0001-0039

问题 In an ERD, a weak/non-identifying relationship is one that connects two strong entities, and is indicated with a dashed line. A strong/identifying relationship is one that connects a strong entity to a weak entity (a weak entity is one that contains the foreign key [FK] from its related entity as a component of its own primary key [PK]), and is indicated by a solid line. My question is, So what? Why is it so important to distinguish between weak/non-identifying relationships versus strong