LINQ (LAMBDA) How do I add another list of objects to my Where? c#

Question

Good afternoon, I’m running a C# Net Core application, using lambda for database context handling. I have one question, and that is: I have a list of objects with these two attributes: Name and Startdate. Something like:

List<Operations> operations = new List<Operations>();
operations.Add(new Operation() { Name: "Exemplo 1", StartDate: "2018-07-02 00:00:00" };
operations.Add(new Operation() { Name: "Exemplo 2", StartDate: "2017-05-01 13:00:00" };

Now I would like to do a lambda in my context, iterating this list with a condition with the operator "OR". Something that would look like this in SQL:

SELECT
    *
FROM
    contact t
WHERE
    (t.OperationName = "Exemplo 1" AND t.ContactDate > "2018-07-02 00:00:00")
    OR (t.OperationName = "Exemplo 1" AND t.ContactDate > "2017-05-01 13:00:00")

But I’m not getting it. The conditions within the parentheses are separated by AND, when they relate to the same object, and separating the objects by OR. I’m using Lambda, something as follows below:

dbContext.Teste.Where(x => x...);

@EDIT: A Fiddle I made to demonstrate my problem: https://dotnetfiddle.net/DqvOx4

In this Fiddle, I can only do Where with the first obj of Operations, but I need to iterate through all objects. Does anyone have any idea how to do this using Lambda?

Answer 1

To use AND and OR with lambda the operator is used && and ||

Let’s assume you have next class:

public class Operation
{
    public string Name { get; set; }
    public DateTime StartDate { get; set; }
}

With this we can create (Simulating database data) a list of operations as follows

List<Operation> operations = new List<Operation>
{
    new Operation() { Name= "Exemplo 1", StartDate= Convert.ToDateTime("2018-07-02 00:00:00") },
    new Operation() { Name = "Exemplo 2", StartDate= Convert.ToDateTime("2017-05-01 13:00:00") },
    new Operation() { Name = "Exemplo 3", StartDate= Convert.ToDateTime("2016-05-01 13:00:00") }
};

Now we will do a search in this list and throw the selected data in another list as follows

List<Operation> operationsDois = operations.Where(x => (x.Name == "Exemplo 1" && x.StartDate == Convert.ToDateTime("2018-07-02 00:00:00")) || (x.Name == "Exemplo 2" && x.StartDate == Convert.ToDateTime("2017-05-01 13:00:00"))).ToList();

Here an example searching by date, will pick from the last 30 days

List<Operation> operationsTres = operations.Where(x => x.StartDate >= DateTime.Now.AddDays(-30) && x.StartDate <= DateTime.Now).ToList();

With this the second list has researched information.

---

When it’s made a Where it will go through all the dice checking which ones you will "marry", to play it on a list you can do something more or less like this:

List<Teste> testes = dbContext.Teste.Where(x => (x.Name == "" && x.StartDate == "") || (x.Name == "" && x.StartDate == "")).ToList();

Answer 2

I managed to solve the problem.

The way a list can be iterated over another, is by using the "Any()" function of the second list, within the condition of the first. Fiddle with the problem solved: https://dotnetfiddle.net/QuXwQZ

TL;DR: Excerpt from the code that solved the problem:

List<Contact> listaResultado = 
contacts
.Where(
    x => 
        operations.Any(
            y => 
                x.OperationName.Equals(y.Name) 
                && x.ContactDate > y.StartDate
        )
).ToList();