blocks|key|948968|text|这听起来像是trigger的工作。基本上，您需要在insert上使用触发器，以便检查新值，如果新值为空字符串，则会导致触发器失败。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|948969|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ms189799.aspx^0|6|7|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

This sounds like a job for a <a href="http://msdn.microsoft.com/en-us/library/ms189799.aspx" rel="nofollow">trigger</a>. Basically, you'd want a trigger on insert such that it checks the new value, and if it's empty string, you cause the trigger to fail.

blocks|key|948992|text|您可以添加一个检查约束，以确保字符串不为空。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|948993|CREATE+TABLE+[dbo].[Foo](
++++[bar]+[nvarchar](50)+NOT+NULL
)

ALTER+TABLE+[dbo].[Foo]+WITH+CHECK+
ADD++CONSTRAINT+[CK_Foo]+CHECK++(([bar]<>N''))|code-block|syntax|javascript|948994|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You could add a check constraint that ensures that the string isn't empty. 

<pre><code>CREATE TABLE [dbo].[Foo](
 [bar] [nvarchar](50) NOT NULL
)

ALTER TABLE [dbo].[Foo] WITH CHECK 
ADD CONSTRAINT [CK_Foo] CHECK (([bar]&lt;&gt;N''))
</code></pre>

blocks|key|733110|text|列值不等于空字符串的check约束如何？比触发器干净一点，它可以用包括NHibernate在内的许多ORM在代码中建模，所以你的应用层可以被告知期待它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|733111|如果做不到这一点，当在应用程序层中分配您永远不希望为空的字段时，请尝试使用NullIfBlank()扩展方法：|733112|public+static+string+NullIfBlank(this+string+input)
{
+++return+String.IsNullOrWhitespace(input)+?+null+:+input;
}|code-block|syntax|javascript|733113|空字符串、空字符串和只包含空格、换行符、制表符等的字符串都将返回为null。现在，这将要求您确保您不会对此字段执行任何简单的连接，以免返回null:+null+%2B+"any+string“==+null。|733114|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

How about a check constraint that the column value doesn't equal an empty string? A bit cleaner than a trigger, and it can be modeled in code using many ORMs including NHibernate, so your app layer can be told to expect it.

Failing that, when assigning the field you never want to be empty up in your application layer, try using a NullIfBlank() extension method:

<pre><code>public static string NullIfBlank(this string input)
{
 return String.IsNullOrWhitespace(input) ? null : input;
}
</code></pre>

Null strings, empty strings, and strings that only contain spaces, newlines, tabspaces, etc will all come back as null. Now, this will require you to make sure you aren't doing any simple concatenations with this field that you don't also want to come back null: null + "any string" == null.

blocks|key|733123|text|使用check约束：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|733124|CREATE+TABLE+SomeTable(+
++++SomeColumn+VARCHAR(50)+NOT+NULL+CHECK+(SomeColumn+<>+'')
)|code-block|syntax|javascript|733125|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use a check constraint:

<pre><code>CREATE TABLE SomeTable( 
 SomeColumn VARCHAR(50) NOT NULL CHECK (SomeColumn &lt;&gt; '')
)
</code></pre>

blocks|key|949132|text|如果MSSQL提供一种清晰的方法来配置空字符串以映射到NULL，那就太好了，因为这是上下文中的含义。但是数据库并不是捕获这个错误的最佳位置，因为如果不将错误提升到另一个抽象级别，就不会有错误处理，在这个抽象级别上，错误应该首先得到处理。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|949133|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It would be nice if MSSQL provided a clean way to configure empty strings to map to NULL, when that's the meaning in context. But the database is not the best place to be trapping this since there's no error handling without raising an error to another abstraction level where it should have been handled in the first place.

I add a <code>NOT NULL</code> constraint on my <code>NVARCHAR</code> column so it couldn't allow any empty values. but unfortunately SQL Server deals with <code>NULL</code> and empty values as two separate values!

So how do I make the server throw an exception when inserting nothing to the column?

I'm thinking using the constraint <a href="http://www.w3schools.com/Sql/sql_check.asp" rel="noreferrer">CHECK</a> but I didn't find any samples when used with <code>NVARCHAR</code> columns!

How to constraint no empty strings on an NVARCHAR column

SQL Server

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我在NVARCHAR列上添加了一个NOT NULL约束，这样它就不能允许任何空值。但不幸的是，SQL Server将NULL和空值作为两个单独的值处理！那么，如何让服务器在不向列插入任何内容时抛出异常呢？我在考虑使用约束，但在使用NVARCHAR列时没有找到任何示例！

问如何约束NVARCHAR列上没有空字符串
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