您可使用该法典:

var query = from d in datacontext.sample where   
                            (TBoxFName.Text=="" || d.FirstName.Contains(TBoxFName.Text.Trim()))
                            &&(TBoxLName.Text == "" || d.LastName.Contains(TBoxLName.Text.Trim()))
                            &&(TBoxFatherName.Text == "" || d.FatherName.Contains(TBoxFatherName.Text.Trim()))
                            && (TBoxPriceDebt.Text == "" || d.DebtPrice.ToString().Contains(TBoxPriceDebt.Text.Trim()))
                            && (CBoxBranch.Text == "" || d.BranchName.Contains(CBoxBranch.Text.Trim()))
                            &&(TBoxDebt.Text == "" || d.DebtId.Contains(TBoxDebt.Text.Trim()))
                            &&(TBoxMeliCode.Text == "" || d.MeliCode.Contains(TBoxMeliCode.Text.Trim()))
                                select d;

I think (it is unclear) you mean something like:

IQueryable<YourType> query = /* some basic query; maybe db.TheTable */

if(!string.IsNullOrEmpty(firstName))
    query = query.Where(row => row.FirstName == firstName);
if(!string.IsNullOrEmpty(lastName))
    query = query.Where(row => row.LastName == lastName);
if(!string.IsNullOrEmpty(fatherName))
    query = query.Where(row => row.FatherName == fatherName);
// etc

var matches = query.Take(50).ToList();

this uses query composition to issue the most appropriate underlying query it can; for example, if this is LINQ-to-SQL and firstName and fatherName are supplied, you would get something like:

select top 50 {some columns} from [dbo].[TheTable] t
where t.FirstName = @p0 and t.FatherName = @p1

<代码>@p0和@p1均为数值参数。

你可以尝试写:

IEnumerable<YourType> query = //data taken from database
var queryWhere = query 
    .Where(x => x.FirstName  == varFirstName   || string.IsNullOrEmpty(x.FirstName ))
    .Where(x => x.LastName == varLastName      || string.IsNullOrEmpty(x.LastName ))
    .Where(x => x.FatherName == varFatherName  || string.IsNullOrEmpty(x.FatherName ))
    //...and so on... 
    .ToList();