C# 无法将值 NULL 插入到 ASP.NET MVC 实体框架中的列中
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Cannot insert the value NULL into column in ASP.NET MVC Entity Framework
提问by Dimo
When trying to use this code:
尝试使用此代码时：
var model = new MasterEntities();
var customer = new Customers();
customer.Sessionid = 25641;
model.Customers.Add(customer);
model.SaveChanges();
I get:
我得到：
{"Cannot insert the value NULL into column 'Sessionid', table 'master.dbo.Column'; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated."}
{"无法将值 NULL 插入列 'Sessionid'，表 'master.dbo.Column'；列不允许为空。INSERT 失败。\r\n语句已终止。"}
The column "Sessionid" is actually the primary key and is marked with [KEY] like this:
“Sessionid”列实际上是主键，并用 [KEY] 标记如下：
public class Customers
{
[Key]
public long Sessionid { get; set; }
public long? Pers { get; set; }
}
So according to thisquestion, it seems as if when the property is marked with [KEY], EF ignores my own declaration of Sessionid since it expects the database to assign the value.
所以根据这个问题，似乎当属性被标记为 时[KEY]，EF 忽略了我自己的 Sessionid 声明，因为它期望数据库分配值。
So how can I solve this? If I remove [KEY]I get the "entity type has no key defined"exception...
那么我该如何解决这个问题呢？如果我删除[KEY]我得到"entity type has no key defined"异常...
采纳答案by Dimo
I solved it by adding [DatabaseGenerated(DatabaseGeneratedOption.None)]like this:
我通过添加[DatabaseGenerated(DatabaseGeneratedOption.None)]这样的方式解决了它：
public class Customers
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public long Sessionid { get; set; }
public long? Pers { get; set; }
}
回答by Code Monkey
You can configure SQL to auto-generate (and auto-increment) the primary key for the table upon inserts. Then just remove the [Key] in C# and you don't need to set the ID in the application manually, the db will generate it for you.
您可以将 SQL 配置为在插入时自动生成（和自动递增）表的主键。然后只需删除C#中的[Key]，您不需要在应用程序中手动设置ID，db会为您生成它。
回答by youHaveAlsoBeenABeginner
I have encountered this problem multiple times while working with Microsoft SQL Serverand I have followed the same way to fix it. To solve this problem, make sure Identity Specificationis set to Yes. Here's how it looks like:
我在使用时多次遇到此问题，Microsoft SQL Server并且我已按照相同的方法修复它。要解决此问题，请确保将Identity Specification设置为Yes。这是它的样子：
In this way the column number auto incrementsas a primary key normally would.
通过这种方式，列号通常会像主键一样自动递增。
HOW?:right-clickthe table that contains the column, choose Design, selectthe primary key and in Column Propertieswindow find Identity Specificationand set it to Yes.
HOW?：右键单击包含该列的表，选择Design，选择主键并在Column Properties窗口中找到Identity Specification并将其设置为Yes。
