C#ADO.NET:空和DBNull的 - 有没有更有效的语法? [英] C# ADO.NET: nulls and DbNull -- is there more efficient syntax?
问题描述
我有一个日期时间?
我试图用 DbParameter
插入到一个字段。我创建的参数,像这样:
DbParameter datePrm = updateStmt.CreateParameter();
datePrm.ParameterName =@change_date;
然后我想把日期时间?
到 dataPrm.Value
,而占<值code>空秒。
我想一开始我会很聪明的:
datePrm.Value = nullableDate?的DBNull.Value;
但失败,出现错误
运营商'?不能应用于类型的操作数的System.DateTime?和System.DBNull
所以我想这只有当第二个参数是第一个参数的不可为空的版本。于是我去了:
datePrm.Value = nullableDate.HasValue? nullableDate.Value:的DBNull.Value;
但是,这并不管用:
有条件的前pression类型无法确定,因为没有'System.DateTime的'和'System.DBNull
之间的隐式转换
但我不希望这些类型之间的转换!
到目前为止,我唯一能得到的工作是:
如果(nullableDate.HasValue)
datePrm.Value = nullableDate.Value;
其他
datePrm.Value =的DBNull.Value;
这真的是唯一的出路,我可以写这篇文章?有没有一种方法使用三元运营商合作,以获得一个班轮?
更新:我真的不明白,为什么?版本无法正常工作。 MSDN说:
的?操作符返回左边的操作数,如果它不为空,否则将返回正确的操作。
这正是我想要的!
UPDATE2:那么这是一种明显的中底:
datePrm.Value = nullableDate? (对象)的DBNull.Value;
啊哈!我发现了一个更有效的解决方案比@ Trebz的!
datePrm.Value = nullableDate? (对象)的DBNull.Value;
I've got a DateTime?
that I'm trying to insert into a field using a DbParameter
. I'm creating the parameter like so:
DbParameter datePrm = updateStmt.CreateParameter();
datePrm.ParameterName = "@change_date";
And then I want to put the value of the DateTime?
into the dataPrm.Value
while accounting for null
s.
I thought initially I'd be clever:
datePrm.Value = nullableDate ?? DBNull.Value;
but that fails with the error
Operator '??' cannot be applied to operands of type 'System.DateTime?' and 'System.DBNull'
So I guess that only works if the second argument is a non-nullable version of the first argument. So then I went for:
datePrm.Value = nullableDate.HasValue ? nullableDate.Value : DBNull.Value;
but that doesn't work either:
Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DateTime' and 'System.DBNull'
But I don't want to convert between those types!
So far the only thing I can get to work is:
if (nullableDate.HasValue)
datePrm.Value = nullableDate.Value;
else
datePrm.Value = DBNull.Value;
Is that really the only way I can write this? Is there a way to get a one-liner using the ternary operator to work?
Update: I don't really get why the ?? version doesn't work. MSDN says:
The ?? operator returns the left-hand operand if it is not null, or else it returns the right operand.
That's exactly what I want!
Update2: Well it was kind of obvious in the end:
datePrm.Value = nullableDate ?? (object)DBNull.Value;
Ah ha! I found an even more efficient solution than @Trebz's!
datePrm.Value = nullableDate ?? (object)DBNull.Value;
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