相当于 SQL IN 运算符的 linq 是什么
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What is the linq equivalent to the SQL IN operator
提问by Luca Romagnoli
With linq I have to check if a value of a row is present in an array.
The equivalent of the sql query:
使用 linq，我必须检查数组中是否存在行的值。
相当于 sql 查询：
WHERE ID IN (2,3,4,5)
How can I do it?
我该怎么做？
采纳答案by David Morton
.Contains
.包含
var resultset = from x in collection where new[] {2,3,4,5}.Contains(x) select x
Of course, with your simple problem, you could have something like:
当然，对于您的简单问题，您可能会遇到以下问题：
var resultset = from x in collection where x >= 2 && x <= 5 select x
回答by Lachlan Roche
Perform the equivalent of an SQL IN with IEnumerable.Contains().
使用IEnumerable.Contains()执行等效的 SQL IN 。
var idlist = new int[] { 2, 3, 4, 5 };
var result = from x in source
where idlist.Contains(x.Id)
select x;
回答by Justin Niessner
db.SomeTable.Where(x => new[] {2,3,4,5}.Contains(x));
or
或者
from x in db.SomeTable
where new[] {2,3,4,5}.Contains(x)
回答by atreeon
Intersect and Except are a little more concise and will probably be a bit faster too.
Intersect 和 except 更简洁一点，也可能会更快一点。
IN
在
collection.Intersect(new[] {2,3,4,5});
NOT IN
不在
collection.Except(new[] {2,3,4,5});
or
或者
Method syntax for IN
IN 的方法语法
collection.Where(x => new[] {2,3,4,5}.Contains(x));
and NOT IN
并且不在
collection.Where(x => !(new[] {2,3,4,5}.Contains(x)));
回答by Nathan Taylor
An IEnumerable<T>.Contains(T)statement should do what you're looking for.
一个IEnumerable<T>.Contains(T)语句应该做你正在寻找的。
回答by Kamal
A very basic example using .Contains()
使用 .Contains() 的一个非常基本的例子
List<int> list = new List<int>();
for (int k = 1; k < 10; k++)
{
list.Add(k);
}
int[] conditionList = new int[]{2,3,4};
var a = (from test in list
where conditionList.Contains(test)
select test);
回答by AndreyAkinshin
You can write help-method:
您可以编写帮助方法：
public bool Contains(int x, params int[] set) {
return set.Contains(x);
}
and use short code:
并使用短代码：
var resultset = from x in collection
where Contains(x, 2, 3, 4, 5)
select x;
回答by user12063853
The above situations work when the Containsfunction is used against primitives, but what if you are dealing with objects (e.g. myListOrArrayOfObjs.Contains(efObj))?
当Contains函数用于原始类型时，上述情况有效，但是如果您正在处理对象（例如myListOrArrayOfObjs.Contains(efObj)）呢？
I found a solution! Convert your efObjinto a string, thats separated by _for each field (you can almost think of it as a CSV representation of your obj)
我找到了解决办法！将您的efObj转换为string，即_每个字段的分隔符（您几乎可以将其视为 obj 的 CSV 表示）
An example of such may look like this:
此类示例可能如下所示：
var reqAssetsDataStringRep = new List<string>();
foreach (var ra in onDemandQueueJobRequest.RequestedAssets)
{
reqAssetsDataStringRep.Add(ra.RequestedAssetId + "_" + ra.ImageId);
}
var requestedAssets = await (from reqAsset in DbContext.RequestedAssets
join image in DbContext.Images on reqAsset.ImageId equals image.Id
where reqAssetsDataStringRep.Contains(reqAsset.Id + "_" + image.Id)
select reqAsset
).ToListAsync();
回答by Shahid
Following is a generic extension method that can be used to search a value within a list of values:
以下是可用于在值列表中搜索值的通用扩展方法：
public static bool In<T>(this T searchValue, params T[] valuesToSearch)
{
if (valuesToSearch == null)
return false;
for (int i = 0; i < valuesToSearch.Length; i++)
if (searchValue.Equals(valuesToSearch[i]))
return true;
return false;
}
This can be used as:
这可以用作：
int i = 5;
i.In(45, 44, 5, 234); // Returns true
string s = "test";
s.In("aa", "b", "c"); // Returns false
This is handy in conditional statements.
这在条件语句中很方便。
