entity-relationship

问题 I know this might sound a bit ridiculous, but I got a doubt that if we can represent relationship between two tables, how the two table's data is related, is there a way to represent relationship like, each registered user has a seperate pagelikes table. To make it more clear about my doubt, let me explain in this way, students enrolling for a few courses, say c, c++, java or others. Then, we can say: Student -(enrols for)- courses which means that student x can register for courses like c, c

问题 I'm kind of stuck working out where I'm going wrong with the below entity framework mapping. What I've done is: a) created a Sqlite database (see below, noting Sqlite doesn't allow FK constraints) b) created a blank Entity Data Mode & then created the model from the database c) issue is then trying to add the Model association so it picks up and uses the "ProcessNameId" column I've created in the database in the USAGES table. I've been trying to use the GUI Table Mapping pane to do this but

问题 Little example about Books and Authors: DB structure: Entities (they were generated form database using symfony2 console commands): Author: /** * Author * * @ORM\Table(name="authors") * @ORM\Entity */ class Author { private $_isCachable = true; /** * @var integer * * @ORM\Column(name="id", type="integer", nullable=false) * @ORM\Id * @ORM\GeneratedValue(strategy="IDENTITY") */ private $id; /** * @var string * * @ORM\Column(name="name", type="string", length=255, nullable=false) */ private

问题 I am new to UML, and I don't quite understand the notation yet. This is my understanding of the diagram. The system has many doctors. Doctors can have many patients; however, patients can only have one doctor. Therefore this is a **One-To-Many** relationship However, I feel like this can also be interpreted as... The system has 1 doctor. That one doctor has many patients. Which is the correct interpretation and why? 回答1: To put it simply: your first interpretation is correct. Each Doctor is

问题 I have a very simple Core data Model comprising of a single Gallery which contains multiple Images. It seems to me that it should be enough for a Gallery to have a one-to-many relationship with Image, but if I don't also establish an inverse relationship from Image back to gallery I get Compiler warnings and errors. From an object-oriented perspective it seems to me that an Image shouldn't know or care if it is in a Gallery or any other ManagedObject so why does the compiler force me to

问题 I'm searching the opposite solution to the question exporting SQL from a Viso diagram. I have the SQL statement for the creation of multiple tables of a MySQL database. Is there a way to use the Reverse-Engineering feature of Visio 2010 to create a diagram thereof? I'm wondering if it is possible to create a Access database from the SQL statement (MySQL) where Visio could connect ... Alternative I'll try to use another MySQL database, create the tables there, and try to connect with Visio to

问题 I have two entities defined: Product: ProductId (PK) Name (not null) Parts: PartId (PK) Name (not null) These have a many-to-many relationship defined between them. In my requirements I need to model another one-to-many relationship between the composite product/part item to some other composite product/part. In certain instances I also need to be able to link product without a part to product/part item. I have modeled it this way: ProductPartLink: ProductPartLinkId (PK) ProductId (not null)

问题 In every tutorial on entity relationship diagrams, I read that specifying a fixed cardinality for a relationship is not allowed. Only an informal comment on the ERD may clarify that the number of pilots is exactly 2 . So, for example, a relationship between flights and pilots where each flight has exactly 2 pilots present, would have to be represented as: <flight> 0..N <------> 1..N <pilot> rather than <flight> 0..N <------> 2 <pilot> My notation is 0..N = optional, many; 1..N = mandatory,

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . I need to generate er diagram from dump of mysql database. I tryed a lot of tools like MySQL WorkBench and they generate only tables, but not connections between them. I need something like this http://www.cacti.net/downloads/docs/sql/database_schema.pdf (last page). Which software could make it? Thanks. 回答1:

问题 I have created a cable database in Access, and I generate a report that has lists the connectors on each end of a cable. Each cable has its own ID, and 2 connector IDs, associated with it. All the connectors are from the same table and is linked to many other tables. I need 2 fields in one table (cable) associated with 2 records in the second table. My solution was to create 2 more tables: A primary connector table and secondary connector table, each of which has all entries from the first