entity-relationship

问题 I have created two table using JPA. i need to give 1-1 relationship between these tables. Can any one tell me how to give relationship between these tables. 回答1: Simply add a column in the table "owning" the relation with a FK constraint. For example: CREATE TABLE MYENTITYA ( ID BIGINT NOT NULL, MYENTITYB_ID BIGINT ); CREATE TABLE MYENTITYB ( ID BIGINT NOT NULL ); ALTER TABLE MYENTITYA ADD CONSTRAINT SQL100326144838300 PRIMARY KEY (ID); ALTER TABLE MYENTITYB ADD CONSTRAINT SQL100326144838430

问题 Below is a link to download a simplified version of my app that has the exact same problem. The plus "Add" button at the top adds a new record that is set at name = 1, qty = 1, and section = 1. Selecting a Cell increments them all to the next number. You can see that both the name and qty update, but the section never updates until you quit the app and start it again. DropBox Download Link I have the following relationship setup in CoreData: In in my TableViewController, I am creating my

问题 My problem relates to DB schema developing and is as follows. I am developing a purchasing module, in which I want to use for purchasing items and SERVICES. Following is my EER diagram, (note that service has very few specialized attributes – max 2) My problem is to keep products and services in two tables or just in one table? One table option – Reduces complexity as I will only need to specify item id which refers to item table which will have an “item_type” field to identify whether it’s a

问题 I'm having trouble modelling this situation. I'm designing a location-based coupon system. A user can define zones and offers and then associate each offer to multiple zones. Also each zone can have more than one offer. So zone and offer have a many to many relationship. The user entity owns both entities. A zone and an offer can only be associated if the same user owns both of them. A diagram can be very helpful. Thanks. 回答1: Assuming a user can own own zones and offers independently from

问题 I am trying to extend the partial classes that the entity framework creates so that I can more easily work with objects like in the code below (please let me know if there's a better or more exceptable way of doing this with the entity framework) Public Sub New(ByVal ProjectID As Integer) Dim proj As Project = (From p In db.Project.Include("Status") Where p.ProjectID = ProjectID).First _ProjectID = proj.ProjectID _ProjectName = proj.ProjectName Me.Status.StatusID = proj.Status.StatusID 'I get

问题 Partial relationships are shown by single lines total relationships are shown by double lines. And in some ER diagrams optional and mandatory relationship is shown by a dotted line and a single line respectively. What is the exact difference of definitions between these concepts? Please use an example if possible. 回答1: Consider the following example: A Patient or a Laboratory may exist independently of any relationship. Some Patients may Purchase Medicine , and some Laboratories may Produce

问题 Is there a program that converts a SQL Server database diagram to er model, or create er model of a database from SQL Server server? 回答1: Within SQL Server, there's the "Database Diagram" feature in each database, in Management Studio. You can create a new diagram from that, and include all (or some) of your tables, so showing where the relationships are, and what the tables are. 回答2: I've used Erwin for 10 years and it works great! Unfortunately it is a bit pricey. Hopefully someone will

问题 I have the following model: I want automatic cascade on delete to work - both because it's convenient, keep my data consistent and because it's well supported in Entity Framework Code First. The problem is that this specific model causes multiple cascade path. This results in SQL Server gives me the following error when I try to generate the database through EF Code First: Introducing FOREIGN KEY constraint 'FK_dbo.Events_dbo.Tournaments_Tournament_Id' on table 'Event' may cause cycles or

问题 I am working on a portion of a manufacturing DB. The business takes in custom orders and builds items to spec. They only build several (let's say 3-10) types of objects, but each type of object is different in the specifications that get recorded. I want to have a master manufacturing table (mfgorders) that lists some common fields and then have it refer to a specifications table that is specific to the entity ordered. I'm not entirely confident this is the right approach. In fact, I'm not

问题 I have many "Users" and each of them will have maximum of 5 "Services". The User should be able to Rate (0-5) on each Service. I would also like to persist the Avg Rating of the Users. This is what I am thinking, but there could be a better way? User id | user_name | dob | ... Service (Fixed number of Services) id |service_description | service_code | avg_rating Rating: id | service_id | user_id | rating (0-5) 回答1: I have created an E/R diagram to depict the way a multiple ratings system can