How do I search in a DataGrid's Items with Multiple dynamic Conditions with LINQ?

I'm using C# WPF and I have DataGrid that fill with MY LIST via SQL Server Data

I have this model :

public class HAVALEHA_MODEL
{
    public double? NUMBER { get; set; }
    public string NAME { get; set; }
    public string CUST_NO { get; set; }
    public long? DATE_N { get; set; }
    public string TAH { get; set; }
    public string MOLAH { get; set; }
    public string SHARAYET { get; set; }
    public int? ANBAR { get; set; }
    public double? FNUMCO { get; set; }
    public double? MAS { get; set; }
}

my list:

public List<HAVALEHA_MODEL> LIST_HAVALEHA { get; set; } = new List<HAVALEHA_MODEL>();

I want to do a search in this DataGrid's Items, but I want the search to be done in such a way that a dynamic condition is automatically added for each field that is filled and finally the created condition is applied,

that is, if the user selects all the fields including the number, Fill in the number, date, etc., and make a condition for each one that is filled in, and finally apply it.

like this :

What have I tried ? :

IEnumerable<HAVALEHA_MODEL> LINQ_SEARCH = null;

if (!string.IsNullOrEmpty(CUST_N_FLD))
{
    LINQ_SEARCH = LIST_HAVALEHA.Where(x => !(x.NAME is null) && x.NAME.ToLowerInvariant().Contains(CUST_N_FLD.ToLowerInvariant()));
}
if (!string.IsNullOrEmpty(NUMBER_FLD))
{
    LINQ_SEARCH = LIST_HAVALEHA.Where(x => !(x.NUMBER is null) && x.NAME.ToLowerInvariant().Contains(NUMBER_FLD.Text.Trim().ToLowerInvariant()));
}

MY_Data_Ggrid.ItemsSource = LINQ_SEARCH.ToList();

that is not correct and it won't work!

It is difficult to clearly and simply explain what I need exactly, please understand

In your if loops, you set

LINQ_SEARCH = LIST_HAVALEHA.Where(...);

, which means that whenever you enter an if loop (i.e. whenever an if loop's condition is truthy), you redefine the value of LINQ_SEARCH based on the single filtering of LIST_HAVALEHA that is performed in that if body.

As far as I can see, LIST_HAVALEHA itself never changes; as a result, the only filtering that is actually applied is the filtering that is applied to LINQ_SEARCH in the very last 'activated' if loop.

Depending on your desired output, I'd suggest one of two approaches to get around this:

1. If you want to display all havaleha items when no filters are applied, you can set LINQ_SEARCH equal to LIST_HAVALEHA prior to applying the filters, and then applying the filters to LINQ_SEARCH in your if loops:

IEnumerable<HAVALEHA_MODEL> LINQ_SEARCH = LIST_HAVALEHA;

if (!string.IsNullOrEmpty(CUST_N_FLD))
{
    LINQ_SEARCH = LINQ_SEARCH.Where(...);
}
if (!string.IsNullOrEmpty(NUMBER_FLD))
{
    LINQ_SEARCH = LINQ_SEARCH.Where(...);
}

MY_Data_Ggrid.ItemsSource = LINQ_SEARCH.ToList();

2. If you rather want to display no havaleha items when noe filters are applied, you could let LINQ_SEARCH be null to begin with, use LIST_HAVALEHA as a 'backup' when applying filters, and use an empty list as a backup when populating MY_Data_Ggrid.ItemsSource:

IEnumerable<HAVALEHA_MODEL> LINQ_SEARCH = null;

if (!string.IsNullOrEmpty(CUST_N_FLD))
{
    LINQ_SEARCH = (LINQ_SEARCH ?? LIST_HAVALEHA).Where(...);
}
if (!string.IsNullOrEmpty(NUMBER_FLD))
{
    LINQ_SEARCH = (LINQ_SEARCH ?? LIST_HAVALEHA).Where(...);
}

MY_Data_Ggrid.ItemsSource = LINQ_SEARCH?.ToList() ?? new List<HAVALEHA_MODEL>();

I find the second approach ...not so nice, but it is at least an option for that specific use case.