entity-relationship

问题 I am having problem with saving the changes to database. I am updating the model A in my controller, however when I save the changes using SaveChanges() I end up having a duplicated item in database for B. After the UpdateModel() is called I inspected the Bs property and it was as I expected however right after the SaveChanges() is called if I inspect the Bs property I will see that the Id is completely different (new Id and new entry). My class is similar to this: public class A {

问题 I'm taking my first steps in Symfony2 entity relations. I have an entity installation, which each has one meter, and one monitor. This translates to a uni-directional relationship, which I defined as such: /** * * @ORM\OneToOne(targetEntity="InfoMeter") * @ORM\JoinColumn(name="meterid", referencedColumnName="id") */ private $meter; /** * * @ORM\OneToOne(targetEntity="InstallationsRtu") * @ORM\JoinColumn(name="monitorid", referencedColumnName="id") */ private $monitor; Each monitor can only be

问题 This question already has answers here : How to store ner result in json/ database (2 answers) Closed 3 years ago . (S (PERSON Rami/NNP Eid/NNP) is/VBZ studying/VBG at/IN (ORGANIZATION Stony/NNP Brook/NNP University/NNP) in/IN (LOCATION NY/NNP)) This is output of NLTK code now i want to store it in json file like import json data = { 'Rami Eid':{'ORGANIZATION': 'Stony Brook University', 'location':'NY'}, 'GuruRaj Bagali':{'job': 'professor', 'location': 'NY'} } I want store chunk tree into

问题 Lets jump to an example that illustrates a table referencing multiple tables : CREATE TABLE Corses ( ID int PRIMARY KEY, ..... ) CREATE TABLE Questions ( ID int PRIMARY KEY, ..... ) CREATE TABLE Answers ( ID int PRIMARY KEY, ..... ) CREATE TABLE Files ( ID INT PRIMARY KEY, Corse_ID INT, Question_ID INT, Answer_ID INT, FOREIGN KEY (Corse_ID) REFERENCES Corses(ID), FOREIGN KEY (Question_ID) REFERENCES Questions(ID), FOREIGN KEY (Answer_ID) REFERENCES Answers(ID) ) The example above illustrates

问题 A company provides transport services to high-ranked staffs. There are 3 tables: DRIVERS, VEHICLES, STAFFS. DRIVERS - license number [PK] - name - language spoken - ... (and so on..) VEHICLES - vehicle ID [PK] - registration number - model - colour - ... and so on... STAFFS - staff ID [PK] - name - position name - ... and so on.... I want to create a new table called ORGANIZE whereby, it will assign a driver and a vehicle to match the needs of the staff. what will be the PK and FKs? 回答1: I've

问题 So I have the following SQL commands for the description below. I am not sure I have the constraints right especially for the foreign keys, and when to use not null and when not too. Can someone verify if the commands are correct, based on the database description? Car Dealerships have a unique business id number, dealership name, city, state, and a unique website URL. The business id is a number in the range from 1000-9999. Salespersons have a first name, last name, age, gender, and a unique

问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 4 years ago . Note: This is a rough copy i didnt include constraints, weak entities, ..., etc yet. I still need to have a solid understanding of this question. Questions: To keep track of what theater company manages performer, what performer is in two theatre companies do i have to make a

问题 Problem Which is correct when join section table with class table OR with course table OR with instructor Table . Details section is group of student classified to ( aa,bb,cc )can take one course or more courses. section can teach in one or more class(lab or class room) . Instructor can teach to more sections and section can have more instructor raltion is many to many and made in third table Inst_Course My ER diagram as following : section table join Database Schema as following : CREATE

问题 I have a Inheritance Hierarchy where Action is parent of ActionCompleted and ActionCancelled. Order class has a zero to one ActionCompleted and ActionCancelled. I have tried TPH and TPT (even tried edmx) but unable to get Entity to understand this relationship between Order and child actions, please suggest how do I map? //Classes public class Order { public int OrderId { get; set; } public string Name { get; set; } public ActionCompleted ACO { get; set; } public ActionCancelled ACA { get;

问题 After this question, I think I will go for Entity-relationship modelling to solve the issue of my image table that serves many other tables. But now I have another bigger problem as there are groups/ categories in each uploaded/ inserted image, page, user, etc. The reason I have these category tables is to allow an admin to change the category name and add more categories in whenever is need. I use category tables to categorise each of them, for instance, categories for image, category_id