Business.cs

public static class EpisodeHelper
{
    // PERFORMANCE AUDIT !!!
    public static IQueryable<Episode> GetEpisodeQueryable(this ERPContext _Context)
    {
        return _Context.Episodes
            .AsNoTracking()
            .Include(a => a.Clinic)
            .Include(a => a.UserAdmitted)
            .Include(a => a.Records)
                .ThenInclude(r => r.UserAppoint)
            .Include(a => a.Records)
                .ThenInclude(r => r.Service)
            .Include(a => a.Invoices);
    }
    
    // PERFORMANCE AUDIT !!!
    public static SearchResult<EpisodeModel> GetEpisodeResults(this IQueryable<Episode> query, string keySearch = "", bool deleted = false, int page = 1, int limit = 10)
    {
        if (!string.IsNullOrEmpty(keySearch))
        {
            query = query.Where(a =>
                (a.PublicTitle != null && ApplicationDBContext.Standardizing(a.PublicTitle).Contains(keySearch)) ||
                (a.UserAdmitted != null && ApplicationDBContext.Standardizing(a.UserAdmitted.FullName).Contains(keySearch)) ||
                (a.UserAdmitted != null && !string.IsNullOrEmpty(a.UserAdmitted.Phone) && a.UserAdmitted.Phone.Contains(phoneSearch)) ||
                (a.Records != null && a.Records.Any(r =>
                    (r.UserAppoint != null && ApplicationDBContext.Standardizing(r.UserAppoint.FullName).Contains(keySearch)) ||
                    (r.Service != null && ApplicationDBContext.Standardizing(r.Service.ServiceName).Contains(keySearch))
                )));
        }
        
        if (deleted)
        {
            query = query.Where(a => a.StatusID == (byte)EpisodeStatusType.Deleted);
        }
        else
        {
            query = query.Where(a => a.StatusID != (byte)EpisodeStatusType.Deleted);
        }

        var totals = query.Count();
        var items = query
            .OrderByDescending(p => p.DateCreated)
            .Skip((page - 1) * limit)
            .Take(limit)
            .Select(EpisodeModel.Convert)
            .ToList();

        return new SearchResult<EpisodeModel>()
        {
            Totals = totals,
            Items = items
        };
    }
}

DbContext.cs

public class ApplicationDBContext : DbContext
{
    public ApplicationDBContext() : base()
    {
    }

    public ApplicationDBContext(DbContextOptions options) : base(options)
    {
        Database.EnsureCreated();
    }

    [DbFunction]
    public static string Standardizing(string input) => throw new NotImplementedException("This method must existed in DB Functions!");
}

Standardizing.sql

USE [EDU]
GO
/****** Object:  UserDefinedFunction [dbo].[Standardizing]    Script Date: 9/15/2022 2:00:21 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[Standardizing] (
 @input nvarchar(max)
)
RETURNS varchar(max)
AS 
BEGIN
	DECLARE @count int;

	DECLARE @withaccents nvarchar(100);
	DECLARE @withoutaccents nvarchar(100);

	DECLARE @result nvarchar(max);
	SELECT @result = @input;

	-- ACCENTS
    SET @withaccents = N'ăâđêôơưàảãạáằẳẵặắầẩẫậấèẻẽẹéềểễệếìỉĩịíòỏõọóồổỗộốờởỡợớùủũụúừửữựứỳỷỹỵýĂÂĐÊÔƠƯÀẢÃẠÁẰẲẴẶẮẦẨẪẬẤÈẺẼẸÉỀỂỄỆẾÌỈĨỊÍÒỎÕỌÓỒỔỖỘỐỜỞỠỢỚÙỦŨỤÚỪỬỮỰỨỲỶỸỴÝ';
    SET @withoutaccents = N'aadeoouaaaaaaaaaaaaaaaeeeeeeeeeeiiiiiooooooooooooooouuuuuuuuuuyyyyyAADEOOUAAAAAAAAAAAAAAAEEEEEEEEEEIIIIIOOOOOOOOOOOOOOOUUUUUUUUUUYYYYY';
    SET @count = LEN(@withaccents);

    WHILE (@count > 0)
	BEGIN
        SET @result = REPLACE(@result, SUBSTRING(@withaccents, @count, 1), SUBSTRING(@withoutaccents, @count, 1));
        SET @count = @count - 1;
	END

    RETURN LOWER(@result);
END

StringExtension.cs

public static class StringExtension
{
    private static readonly string[] VietnameseSigns = new string[]
    {
        "aAeEoOuUiIdDyY",
        "áàạảãâấầậẩẫăắằặẳẵ",
        "ÁÀẠẢÃÂẤẦẬẨẪĂẮẰẶẲẴ",
        "éèẹẻẽêếềệểễ",
        "ÉÈẸẺẼÊẾỀỆỂỄ",
        "óòọỏõôốồộổỗơớờợởỡ",
        "ÓÒỌỎÕÔỐỒỘỔỖƠỚỜỢỞỠ",
        "úùụủũưứừựửữ",
        "ÚÙỤỦŨƯỨỪỰỬỮ",
        "íìịỉĩ",
        "ÍÌỊỈĨ",
        "đ",
        "Đ",
        "ýỳỵỷỹ",
        "ÝỲỴỶỸ"
    };

    public static string RemoveAccents(this string text)
    {
        if (String.IsNullOrEmpty(text))
        {
            return string.Empty;
        }

        for (int i = 1; i < VietnameseSigns.Length; i++)
        {
            for (int j = 0; j < VietnameseSigns[i].Length; j++)
                text = text.Replace(VietnameseSigns[i][j], VietnameseSigns[0][i - 1]);
        }
        return text;
    }

    public static string Standardizing(this string text)
    {
        if (String.IsNullOrEmpty(text))
        {
            return string.Empty;
        }
        return text.RemoveAccents().ToLower();
    }
}