How to make LINQ execute a (SQL) LIKE range search

I am in big need of help, i have been trying to do this for some time now.

So I have this Query:

Select name from BlaBlaBla

order by 

case when name like '9%' then 1 end,
case when name like '8%' then 1 end,
case when name like '7%' then 1 end,
case when name like '6%' then 1 end,
case when name like '5%' then 1 end,
case when name like '4%' then 1 end,
case when name like '3%' then 1 end,
case when name like '2%' then 1 end,
case when name like '1%' then 1 end,
case when name like '0%' then 1 end,

name

And I want to implement it in a new C#, Asp.Net, class, in my Solution, to the Domain Project, so it will be an OrderType Filter, for some function...

for now I have this:

var param = Expression.Parameter(typeof(T), "item");

var paramName = Expression.Property(param, "Name");
var regexMatch = Expression.Constant("^[0-9]");
var startsWithDigit = Expression.Call(typeof(Regex), "IsMatch", 
                                             null, paramName);

var lambda = Expression.Lambda<Func<T, bool>>(startsWithDigit, 
                                              param);

return namesList.OrderBy(lambda)
           .ThenBy(BlaBla1())
           .ThenByDescending(BlaBla2())
           .ThenByDescending(BlaBla3())
           .ThenBy(BlaBla4());

But it tells me, that Expression does not contain "IsMatch" method.

Can you please help me? Thank you!!!

The problem here is that expressions containing Regex can't be translated to SQL, so even when you'd succeed in building a correct expression, you can't use it in LINQ to a SQL backend. However, SQL's LIKE method also supports range wildcards like [0-9], so the trick is to make your LINQ translate to SQL containing a LIKE statement.

LINQ-to-SQL offers the possibility to use the SQL LIKE statement explicitly:

return namesList.OrderBy(r => SqlMethods.Like(r.Name, "[0-9]%")) ...

This SqlMethods class can only be used in LINQ-to-SQL though. In Entity Framework there are string functions that translate to LIKE implicitly, but none of them enable the range wildcard ([x-y]). In EF a statement like ...

return namesList.OrderBy(r => r.Name.StartsWith("[0-9]")) ...

... would translate to nonsense:

[Name] LIKE '~[0-9]%' ESCAPE '~'

I.e. it vainly looks for names starting with the literal string "[0-9]". So as long as you keep using LINQ-to-SQL SqlMethods.Like is the way to go.

In Entity Framework 6.1.3 (and lower) we have to use a slightly different way to obtain the same result ...

return namesList.OrderBy(r => SqlFunctions.PatIndex("[0-9]%", c.Name) == 1) ...

... because PatIndex in SqlFunctions also supports range pattern matching.

But in Entity Framwork 6.2 we're back on track with LINQ-to-SQL because of the new DbFunctions.Like function:

return namesList.OrderBy(r => DbFunctions.Like(r.Name, "[0-9]%")) ...

Finally, also Entity Framework core has a Like function:

return namesList.OrderBy(r => EF.Functions.Like(r.Name, "[0-9]%")) ...

How to make LINQ execute a (SQL) LIKE range search

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