SingleOrDefault异常处理 [英] SingleOrDefault exception handling

问题描述

我有一个萨姆代码，它会调用SingleOrDefault方法3次，并在任何序列具有多个匹配元素的情况下记录异常.

I have a samle code which calls SingleOrDefault method 3 times and logs exception if any sequence has more than one matching element.

如果我想检查这段代码的哪一部分引发异常，问题就开始了.

The problem starts if I want to check which part of this code throws exception.

是否可以从此异常中获取一些有用的信息，例如谓词参数或收集类型以获取更详细的跟踪信息?

Is it possible to get some useful information from this exception like predicate parameter or collection type for more detailed trace?

-序列包含多个匹配元素.集合IEnumrable | ParamType |param {谓词para to toString()}

 public void GetSingleOrDefaultTest(){

    try{

        var user = Users.SingleOrDefault(e => e.Id == 1);

        var profile = UserProfiles.SingleOrDefault(e => e.Id == 1);

        var profile2 = UserProfiles.SingleOrDefault(e => e.Id == 2);


    } catch(InvalidOperationException ex){
        Log(ex);
    }

}

推荐答案

如果您想知道哪个语句发出了错误，则必须单独检查它们.在每个 SingleOrDefault 调用上捕获 InvalidOperationException ，并将其包装在新的异常中，您可以在其中填充其他信息.

If you want to know which of the statement issues the error you have to check them separateley. Catch the InvalidOperationException on every SingleOrDefault invocation and wrap it in a new exception which you can fill with additional information.

try
{
    User user;
    UserProfile profile;
    UserProfile profile2;

    try
    {
        user = Users.SingleOrDefault(e => e.Id == 1);
    }
    catch (InvalidOperationException ex)
    {
        throw new InvalidOperationException("User lookup for Id = 1 failed", ex);
    }

    try
    {
        profile = UserProfiles.SingleOrDefault(e => e.Id == 1);
    }
    catch (InvalidOperationException ex)
    {
        throw new InvalidOperationException("User profile lookup for Id = 1 failed", ex);
    }

    try
    {
        profile2 = UserProfiles.SingleOrDefault(e => e.Id == 2);
    }
    catch (InvalidOperationException ex)
    {
        throw new InvalidOperationException("User profile lookup for Id = 2 failed", ex);
    }

    // work with user, profile and profile2
}
catch(InvalidOperationException ex)
{
    Log(ex);
}

您还可以通过以下方法封装单个try捕获

You also can encapsulate the single try catches by the following

private static T GetSingleOrDefault<T>(IEnumerable<T> collection, Expression<Func<T, bool>> predicate)
{
    try
    {
        return collection.SingleOrDefault(predicate.Compile());
    }
    catch (InvalidOperationException e)
    {
        var message = string.Format(
            "{0} (Collection: {1}, param: {2})",
            e.Message,
            collection.GetType(),
            predicate);

        throw new InvalidOperationException(message);
    }
}

使您的代码看起来像

try
{
    var user = GetSingleOrDefault(Users, e => e.Id == 1);

    var profile = GetSingleOrDefault(UserProfiles, e => e.Id == 1);

    var profile2 = GetSingleOrDefault(UserProfiles, e => e.Id == 2);

    // work with user, profile and profile2
}
catch(InvalidOperationException ex)
{
    Log(ex);
}

这会产生类似消息

System.InvalidOperationException:序列包含多个匹配元素(集合:IEnumerable`1 [User]，参数:e => e.Id == 1)

System.InvalidOperationException: Sequence contains more than one matching element (Collection: IEnumerable`1[User], param: e => e.Id == 1)

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