How to use LINQ query in C# to filter data by empty or single string or string array

Question

I have a string parameter 'type' to my method, which can be null, single value or multiple values separated by comma as follows:

string type=null; //should return all rows
string type="java"; //should return data with java 
string type="xamarin,java,c#"; //should return data with all these 3 options
string type="invalid"; //should return null

I need to return all rows if type is empty else return only the rows matching the string array.

I am using following LINQ in my server side cs file:

public object filter(string type)
{
var models = context. /// get data from db, with id,Date,type,comment as columns
return models.Where(v=> string.IsNullOrEmpty(type) ? true : type.Split(',').Contains(v.type)
.OrderByDescending(a => a.Date).ToList();

}

When i pass null, it returns all row - seems working

When i pass type separated by comma, it return rows of all types - seems working

When i pass invalid type, it should return zero rows (Not working)

I am expecting a clean and single line solution.

Answer 1

You want this result

string type="invalid"; //should return null

but in you code this condition is not processed

return type.Split(',').Contains("invalid") ? null : models
       .Where(v=> string.IsNullOrEmpty(type) ? true : type.Split(',').Contains(v.type)
       .OrderByDescending(a => a.Date)
       .ToList();

Answer 2

谢谢朋友，它适用于任何情况。

return models.Where(v => string.IsNullOrWhiteSpace(type) ? true : type.Split(',').Contains(v.type) ).OrderByDescending(a => a.Date).ToList();