c# lambda take FirstOrDefault property if it is not null

Question

I need to check if FirstOrDefault() is not null, and if not, take some property. My best bet is:

var results = Database.Set<Pizzas>().Select(x => new PizzaViewModel
{
    Base = Database.Set<Bases>().FirstOrDefault(y => y.Id == x.Base.Id) != null ? Database.Set<Bases>().FirstOrDefault(y => y.Id == x.Base.Id).Name : null
}).ToList();

Is there better way to do this?

@BalagurunathanMarimuthu Again, that is not a duplicate. Don't throw duplicates that are not an answer to the question. — Patrick Hofman, Jul 03 '17 at 10:07
This looks like a custom implemented outer join. You might consider read into [outer joining](https://stackoverflow.com/questions/3404975/left-outer-join-in-linq). — Jeroen van Langen, Jul 03 '17 at 10:09
@BalagurunathanMarimuthu dublicate you provided doesn't answer my question, since all answers provide similar queries to mine — mazas17, Jul 03 '17 at 10:10

Patrick Hofman · Accepted Answer · 2017-07-03T10:08:04.650

5

You can use null propagation operator on FirstOrDefault():

Base = Database.Set<Bases>().FirstOrDefault(y => y.Id == x.Base.Id)?.Name

edited Jul 03 '17 at 10:08

answered Jul 03 '17 at 10:06

Patrick Hofman

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Its fine to get one property, how to achieve `take some properties`/? let it be some `name` and `age` – sujith karivelil Jul 03 '17 at 10:07
"some property" is singular, right? @un-lucky "properties" is plural. – Patrick Hofman Jul 03 '17 at 10:08
1

Its probably worth mentioning the c# version requirement - some people are for various reasons stuck using older versions that don't support this. :( – Chris Jul 03 '17 at 10:09
Try to use `Find(...)` instead of `FirstOrDefault(...)` if possible. – Fruchtzwerg Jul 03 '17 at 10:09
1

Why? There is nothing to `Find`... This code does what it should. – Patrick Hofman Jul 03 '17 at 10:09
Hava a look at https://stackoverflow.com/questions/14032709/performance-of-find-vs-firstordefault – Fruchtzwerg Jul 03 '17 at 10:10
@PatrickHofman: Yep, Then how can I use this code to retrieve `.Name` and `.Age` properties? – sujith karivelil Jul 03 '17 at 10:11
That is not the question. The questions is "property". @un-lucky – Patrick Hofman Jul 03 '17 at 10:12

score 3 · Answer 2 · answered Jul 03 '17 at 10:18

Since someone mentioned multiple properties I'll add this in, the let allows us to keep the base so that we can query it for multiple things, and the null propagation operator allows us to make sure we're not breaking if there was no base found.

var bases = Database.Set<Bases>();
var results =
    (from pizza in Database.Set<Pizzas>()
    let pizzaBase = bases.FirstOrDefault(pizzaBase => pizzaBase.Id == pizza.Base.Id)
    select new PizzaViewModel {
        Base = pizzaBase?.Name,
        BaseIngredients = pizzaBase?.Ingredients
    }).ToList();

score 0 · Answer 3 · answered Jul 03 '17 at 10:09

0

You can do it this way for C# < 6.0:

Base = Database.Set<Bases>().Where(y => y.Id == x.Base.Id)
                            .Select(y=> y.Name).FirstOrDefault();

Otherwise, you can use the Null-Conditional Operator (?) operator before .Name

answered Jul 03 '17 at 10:09

Zein Makki

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c# lambda take FirstOrDefault property if it is not null

3 Answers3