Query about Entity Framework caching

Question

Lets say I have these three methods:

public Customer GetCustomerByCustomerGuid(Guid customerGuid)
{
    return GetCustomers().FirstOrDefault(c => c.CustomerGuid.Equals(customerGuid));
}

public Customer GetCustomerByEmailAddress(string emailAddress)
{
    return GetCustomers().FirstOrDefault(c => c.EmailAddress.Equals(emailAddress, StringComparison.OrdinalIgnoreCase));
}

public IEnumerable<Customer> GetCustomers()
{
    return from r in _customerRepository.Table select r;
}

//_customerRepository.Table is this:
public IQueryable<T> Table
{
    get { return Entities; }
}

Would this cause a query to the database each time I make a call to GetCustomerByEmailAddress() / GetCustomerByCustomerGuid() or would EF cache the results of GetCustomer() and query that for my information?

On the other hand, would it just cache the result of each call to GetCustomerByEmailAddress() / GetCustomerByCustomerGuid()

I am trying to establish the level of manual caching I should go to, I really dislike running more SQL queries than are absolutely necessary.

Anthony Chu · Accepted Answer · 2014-02-11 22:56:20Z

4

Yes, it'll query the database every time.

Your concern should be to optimize your code so that it only queries for and returns the record you need. Right now it's pulling back the entire table and then you're filtering it with FirstOrDefault().

Change public IEnumerable<Customer> GetCustomers() to public IQueryable<Customer> GetCustomers() to make it more efficient.

edited Feb 11, 2014 at 22:56

answered Feb 11, 2014 at 22:45

Anthony Chu

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16 Comments

evanmcdonnal Over a year ago

That's not how LINQ to EF works. The LINQ Provider is smart enough to translate FirstOrDefault() into select top 1. Basically, any query methods used for a LINQ to EF query that have equivalent SQL functions will be executed as SQL in favor of operating on the result set in C#.

Anthony Chu Over a year ago

It would if it were returning an IQueryable rather than IEnumerable.

webnoob Over a year ago

@evanmcdonnal - That was my understanding as well. The query is generated based on the full LINQ query.

webnoob Over a year ago

@AnthonyChu - In my case _customerRepository.Table is IQueryable<> but the poster would not of known that.

evanmcdonnal Over a year ago

@AnthonyChu how do you know the type returned by GetCustomers()?

|

Community · Accepted Answer · 2017-05-23 12:20:40Z

1

It will result in a call to the database every time. I actually asked a similar question earlier today and you can see more here: Why does Entity Framework 6.x not cache results?

edited May 23, 2017 at 12:20

CommunityBot

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answered Feb 11, 2014 at 22:43

Adam Modlin

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5 Comments

webnoob Over a year ago

Ah I see. Out of interest how did you see if EF was hitting the DB or not?

Adam Modlin Over a year ago

I used SQL Server Profiler to trace all calls to my database.

webnoob Over a year ago

I knew something like that existed but couldn't see it in SQL Express (which I use at home). I'll look a little deeper.

Adam Modlin Over a year ago

I guess that's not part of SQL Express. But it will definitely call the database every single time. I was dealing with this today unfortunately.

webnoob Over a year ago

.Find() it is then. Thanks for the information, I'll mark this as the answer (edit: in 4 minutes :) ).

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