Linq查询（过滤器，在哪里，如果）

Question

I want to put the variables that are filled in question in the where condition. How can I do with Linq?

Running query;

  query = db.Kisi.Where(item => item.KAYITTIPI == registerType)
           .Where(item => item.ADI.Contains(name))
           .Where(item => item.SOYADI.Contains(surname))
           .Where(item => item.UNVAN.Contains(title))
           .OrderBy(item => item.ID)
           .Skip(page)
           .Take(top)
           .ToList();

I want to do;

var query = db.Kisi.Where(item => item.KAYITTIPI == registerType)
                if (String.IsNullOrEmpty(name))
                {
                   .Where(item => item.ADI.Contains(name))
                }
                 else if (String.IsNullOrEmpty(surname))
                {
                    .Where(item => item.SOYADI.Contains(surname))
                }

                 .Where(item => item.UNVAN.Contains(title))
                 .OrderBy(item => item.ID)
                 .Skip(page)
                 .Take(top)
                 .ToList();

Error;

State Error CS0103 The name 'Where' does not exist in the current context 

Answer 1

You can compose your LINQ query in separate statements and they won't be executed until you call ToList :

IQueryable<Kisi> query = db.Kisi.Where(item => item.KAYITTIPI == registerType);

if (!String.IsNullOrEmpty(name))
{
   query = query.Where(item => item.ADI.Contains(name))
}
if (!String.IsNullOrEmpty(surname))
{
    query = query.Where(item => item.SOYADI.Contains(surname))
}

var result = query.Where(item => item.UNVAN.Contains(title))
                  .OrderBy(item => item.ID)
                  .Skip(page)
                  .Take(top)
                  .ToList();

Answer 2

Why not put all your expressions in one boolean expression?

var result = db.Kisi.Where(item => (item.KAYITTIPI == registerType)
    && (!String.IsNullOrEmpty(name)) || item.ADI.Contains(name))
    && (!String.IsNullOrEmpty(surname) || item.SOYADI.Contains(surname))
    && item.UNVAN.Contains(title))
    .OrderBy(...)
    .Skip(...)
    .Take(...);