Speaking of Select
- Sean
So like Where and other fine Extension methods, Select allows you to either give it a lambda expression like so:
List<String> newList = userList.Select(user => user.Name);
Or
List<Int32> newList = userList.Select(user => user.ID);
So either you get a list of Names or IDs. What the hell do you care? Well if you are capable of breathing, you should also notice that one list is a list of strings the other a list of integers. What if you wanted a generic select method? Well for starters you would do something like this:
public List<String> SelectFromUserList(Func<User, String> selectMethod, List<User> userList) { return userList.Select(selectMethod).ToList(); }
Where the select method for a user name would be something like this:
List<String> nameList = SelectFromUserList(currentUser => currentUser.UserName, userList);
Sweet... oh wait, that only works if I want a list strings. Great if I wanted LastName, FirstName, ect but sucks if I wanted an integer ID.
List<String> nameList = SelectFromUserList(currentUser => currentUser.UserID, userList); //BOOM
But wait, you can do that!
public List<K> SelectUserNameList<K>(Func<User, K> selectMethod, List<User> userList) { return userList.Select(selectMethod).ToList(); }
Aw snap, now I can get a list of anything I want, well at least a one type, one dimensional array. By the way, this is the first step in probably a series of posts that will end up with a much cleaner way of doing this.
Like versus Contains in Linq
- Sean
So have to figure this one out. Say you have:
private static Expression<Func<User, Boolean>> WhereLikeFirstNameLastNameUserName(String name) { return currentUser => SqlMethods.Like(currentUser.UserName, "%" + name + "%") || SqlMethods.Like(currentUser.FirstName, "%" + name + "%") || SqlMethods.Like(currentUser.LastName, "%" + name + "%"); }
And
private static Expression <Func<User, Boolean>> WhereLikeFirstNameLastNameUserNameWithoutLike(String name) { return currentUser => currentUser.UserName.Contains(name) || currentUser.FirstName.Contains(name) || currentUser.LastName.Contains(name); }
The first one should look familiar, its part of the "dynamic" linq stuff I've been posting. Now guess which one gives me this SQL when profiled:
exec sp_executesql N 'SELECT [t0].[UserID], [t0].[FirstName], [t0].[LastName], [t0].[Password], [t0].[UserName], [t0].[UserTypeID] FROM [dbo].[User] AS [t0] WHERE ([t0].[UserName] LIKE @p0) OR ([t0].[FirstName] LIKE @p1) OR ([t0].[LastName] LIKE @p2) ORDER BY [t0].[UserName]', N'@p0 varchar(3), @p1 nvarchar(3), @p2 nvarchar(3)', @p0='%s%', @p1=N'%s%', @p2=N'%s%'
If you answered both, you are correct or you looked ahead for the answer and therefore are a tool. Now which do you think that...
query.ToList()
Produces the correct list? If you answered Contains, then you are correct again. If you are a tool, you probably looked ahead again...
Why is this? I HAVE NO IDEA... Something I have to look into for sure.
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