How to use LINQs Include in SQL - sql

Question

In LINQ I have written a simple query where I am searching for an animal using the ID property. However, I am also including the Farm the animal belongs using the Include property.
I want to write the same LINQ query in SQL where I can include Farm. How can I include Farm using SQL. I have an incomplete SQL syntax below. Can anyone help me out.
LINQ
await _dbContext.Animals.Where(x => x.id == 1)
.Include(x => x.Farm)
.ToListAsync();
SQL
select * from Animals where id = 1;

Answer 1

Apparently your database has a table with Animals and a table with Farms. There seems to be a one-to-many relation between Animals and Farms: on every Farm live zero or more Animals; every Animal lives on exactly one Farm, namely the Farm that the foreign key refers to.
I think you will have classes similar to the following:
class Farm
{
public int Id {get; set;}
public string Name {get; set;}
... // etc
// Every Farm has zero or more Animals (one-to-many)
public virtual ICollection<Animal> {get; set;}
}
class Animal
{
public int Id {get; set;}
public string Name {get; set;}
... // etc
// Every Animal lives on exactly one Farm, using foreign key
public int FarmId {get; set;}
public virtual Farm Farm {get; set;}
}
I want to write the same LINQ query in SQL where I can include Farm.
A small trick: if you want to know the SQL code generated by Entity Framework, use property DbContext.Database.Log.
using (var dbContext = new DbContext())
{
// Log generated SQL to debug window:
dbContext.Database.Log = System.Diagnostics.Debug.Write;
// execute your LINQ:
var fetchedAnimals = _dbContext.Animals.Where(x => x.id == 1)
.Include(x => x.Farm)
.ToList();
}
Write your own SQL
You'll have to join Animals with Farms, and keep only the Animal with ID = 1:
See SQL Join
// Select only the properties of Animals and Farms that you actually plan to use
SELECT Animals.Id, Animals.Name, ...,
Farms.Id, Farms.Name, ...
FROM Animals INNER JOIN Farms
ON Animals.FarmId = Farm.Id
WHERE Animals.Id = 1
You should not use "" to fetch everything. If Farm [10] Has 5000 Chickens, then every Chicken will have a foreign key with a value 10. If you use "" you will transfer this value 10 more than 5000 times, while you already know the value of the foreign key.
There's room for improvement
When using entity framework to fetch data, always use Select, and select only the properties that you plan to use, even if you Select all properties. Only omit Select and / or use Include if you plan to change / update the fetched data.
The reason is, that fetching data without using Select is not very efficient.
If you fetch data without using Select, entity framework will put the fetched item in the DbContext.ChangeTracker, together with a copy of the fetched item. You get a reference to the copy. Whenever you change properties of the fetched item, you change the copy in the ChangeTracker. When you call DbContext.SaveChanges, the original is compared with the copy, property per property to see which properties are changed, and thus need to be updated in the database.
So if you don't plan to change the fetched data, it would be a waste of processing power to put this data AND a copy in the ChangeTracker. Hence: always use Select, unless you plan to update the fetched data.