relational-database

问题 I want to model a situation and I´m having real trouble handling it. The domain is like this: There are Posts, and every post has to be associated one to one with a MediaContent. MediaContent can be a picture or a video (for now, maybe music later). So, what I have is: mediacontents/models.py class MediaContent(models.Model): uploader = models.ForeignKey(User) title = models.CharField(max_length=100) created = models.DateTimeField(auto_now_add=True) def draw_item(self): pass class Meta:

问题 Say you have an simple CRM system with customers and orders. If a customer changes his name, will you prefer that the old historical orders get the new name as well, or do you copy it to a string value on the order to preserve the accuracy? I doubt there is an answer that covers all situations, but I'm struggling with deciding where I can accept the historical data to be changed and where I cannot accept it. Generally I'm using the thought that if it can be printed, it must be printable again

问题 Background: Two projects (A & B) under design at the same time both needs a new table(called DocumentStore ) to store document/file under postgres. But business logic around the document storage are different between project A & B, this means relationship around DocumentStore are different between A & B. Let's make this a bit more concrete, see example below: The Document storage table structure looks the same without constraints/ foreign Keys: Table DocumentStore DocUUID //unique Id for this

问题 I apologize for the amount of code but I just need some confirmation of my mapping and usage of [ForeignKey("XXX") is correct or not. In classes like Department and Depot do I need the lines public int DepartmentID { get; set; } or do they automatically number themselves when data is inserted in the database. (DepartmentID = 1 (Human Resources), DepotID = 2 (Los Angeles) This is my Entity Diagram. User.cs public class User { public int UserID { get; set; } [StringLength(50, MinimumLength = 1)

问题 I have this many-many DataMapper/MySQL setup with Torrent and Tag, as follows: class Torrent include DataMapper::Resource property :id, Serial property :name, String property :magnet, Text property :created_at, DateTime has n, :tags, :through => Resource end class Tag include DataMapper::Resource property :id, Serial property :name, String property :hits, Integer has n, :torrents, :through => Resource end When trying to destroy a torrent, however, via Torrent.first.destroy or something

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 regards to SQLite , What is the difference between REFERENCES with, or without a FOREIGN KEY? What is the difference between this CREATE TABLE players_set ( _id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, player_id INTEGER REFERENCES players ( _id ) ON DELETE CASCADE, players_set_id INTEGER REFERENCES players_set_names ( _id ) ); and this: CREATE TABLE players_set ( _id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, player_id INTEGER, players_set_id INTEGER REFERENCES players_set_names ( _id

问题 I have a small database that is used to track parts. for the sake of this example the table looks like this: PartID (PK), int PartNumber , Varchar(50), Unique Description , Varchar(255) I have a requirement to define that certain parts are classified as similar to each other. To do this I have setup a second table that looks like this: PartID , (PK), int SecondPartID , (PK), int ReasonForSimilarity , Varchar(255) Then a many-to-many relationship has been setup between the two tables. The

问题 Does anyone know if there is any speed difference (obviously for tables that are sizable enough) between these two queries: SELECT field FROM table WHERE primary_key = "a particular value" or: SELECT field FROM table WHERE primary_key = "a particular value" LIMIT 0,1 I should note that the primary_key field is actually a primary key. Now LIMIT 0,1 does help when a query would otherwise carry on to find other matches. I'm assuming though that when a primary key is involved it should

问题 I have this table CREATE TABLE [dbo].[CityMaster]( [CityID] [int] NOT NULL, [City] [varchar](100) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL, [BranchId] [varchar](10) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL CONSTRAINT [DF__CityM__Branc__74444068] DEFAULT ((0)), [ExternalBranchId] [varchar](max) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, CONSTRAINT [PK_CityMaster] PRIMARY KEY CLUSTERED ( [City] ASC, [BranchId] ASC ), CONSTRAINT [uk_citymaster_cityid_branchid] UNIQUE NONCLUSTERED (