// C# Eval Expression

// Doc: https://eval-expression.net/my-first-linq-dynamic

​

// @nuget: Microsoft.EntityFrameworkCore.SqlServer

// @nuget: Z.Expressions.Eval

​

/*

## Use LINQ Dynamic with a WhereDynamic method

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The `Where` clause cannot have a dynamic expression. However, the C# Eval Expression library lets you easily achieve this behavior using the `WhereDynamic` method, which, under the hood, creates the lambda expression and call the `Where` method. So our library doesn't mimic and try to interpret the expression but instead really calls the `Where` LINQ method.

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To use our method, you first must add the `using System.Linq;` directive to see LINQ Dynamic extension methods.

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In this example, we assume a typical scenario where a developer uses EF Core and needs to filter a customer list depending on a custom filter entered by the end-user input. We will filter customers in the database to return only active customers who have logged in since the last month.

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As you can see in our example, you can pass the `input parameters` of the lambda expression in 2 different ways:

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- Outside the expression

- Inside the expression

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There is no "recommended way" to pass it, as both solutions are valid and supported. So uses the easiest and more readable way for you.

​

See more: https://eval-expression.net/my-first-linq-dynamic

*/

​

using System;

using System.Linq;

using Z.Expressions;

using Microsoft.EntityFrameworkCore;

using Microsoft.Data.SqlClient;

​

public class Program

{

    public static void Main()

    {

        using (var context = new EntityContext())

        {

            context.Database.EnsureCreated();

        }

        // GENERATE Data

        using (var context = new EntityContext())

        {

            context.Customers.Add(new Customer() { Name ="Customer_A", Status = CustomerStatus.IsActive, LastLogon = DateTime.Now.AddDays(-10) });

            context.Customers.Add(new Customer() { Name ="Customer_B", Status = CustomerStatus.IsActive, LastLogon = DateTime.Now.AddDays(-50) });

            context.Customers.Add(new Customer() { Name ="Customer_C", Status = CustomerStatus.IsDeleted, LastLogon = DateTime.Now.AddDays(-10) });

            context.Customers.Add(new Customer() { Name ="Customer_D", Status = CustomerStatus.IsActive, LastLogon = DateTime.Now.AddDays(-15) });

            context.SaveChanges();  

        }

        using (var context = new EntityContext())

        {

            // var customers = context.Customers.Where(x => x.Status == 0 && x.LastLogon >= DateTime.Now.AddMonths(-1)).ToList();

            var customers = context.Customers.WhereDynamic(x => "x.Status == 0 && x.LastLogon >= DateTime.Now.AddMonths(-1)").ToList();

            FiddleHelper.WriteTable(customers);

        }

        using (var context = new EntityContext())

        {

            // var customers = context.Customers.Where(x => x.Status == 0 && x.LastLogon >= DateTime.Now.AddMonths(-1)).ToList();

            var customers = context.Customers.WhereDynamic("x => x.Status == 0 && x.LastLogon >= DateTime.Now.AddMonths(-1)").ToList();

            FiddleHelper.WriteTable(customers);

        }

    }

    public class EntityContext : DbContext

    {

        public EntityContext() 

        {

        }

​

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

        {

            optionsBuilder.UseSqlServer(new SqlConnection(FiddleHelper.GetConnectionStringSqlServer()));

​

            base.OnConfiguring(optionsBuilder);

        }

        public DbSet<Customer> Customers { get; set; }

    }

    public class Customer

    {

        public int CustomerID { get; set; }

        public string Name { get; set; }

        public CustomerStatus Status { get; set; }

        public DateTime LastLogon { get; set; }

    }

    public enum CustomerStatus

    {

        IsActive = 0,

        IsDeleted = 1,

        IsSuspended = 2

    }

}