What is difference between ToList() & AsQueryable()

Tridip Bhattacharjee

8y18.3kLINQ

please tell me What is difference between ToList() & AsQueryable() ?

see the code with AsQueryable()

var source = (from customer in _context.CustomerTBs.
OrderBy(a => a.Country)
select customer).AsQueryable();

tell me when above code will execute then records will be fetch from db or not ?

var source = (from customer in _context.CustomerTBs.
OrderBy(a => a.Country)
select customer).ToList();

when to use AsQueryable() and when to use ToList() ?

looking for answer in details. thanks

5 Replies

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Brajesh Kumar8y ago
Accepted answer
Hi Tridip

May be this coul help you .

AsQueryable just creates a query, the instructions needed to get a list. You can make futher changes to the query later such as adding new Where clauses that get sent all the way down to the database level.

AsList returns an actual list with all the items in memory. If you add a new Where cluse to it, you don't get the fast filtering the database provides. Instead you get all the information in the list and then filter out what you don't need in the application.

So basically it comes down to waiting until the last possible moment before committing yourself

What's the use?

ToList – which converts an IEnumerable to a List – is often used for this purpose as well. The advantage of using AsEnumerable vs. ToList is that AsEnumerable does not execute the query. AsEnumerable preserves deferred execution and does not build an often useless intermediate list.
On the other hand, when forced execution of a LINQ query is desired, ToList can be a way to do that.

AsQueryable can be used to make an enumerable collection accept expressions in LINQ statements. See here for more details: Do i really need use AsQueryable() on collection?.

Enjoy
Brajesh Kumar8y ago
@ Tridip ,filter will occur on whatever data will comes from the first query.
Tridip Bhattacharjee8y ago
@Brajesh you said -- AsList returns an actual list with all the items in memory. If you add a new Where cluse to it, you don't get the fast filtering the database provides.

see the second code

first line
-------------
var ctx = new SchoolDBEntities()
var student = (from s in ctx.Students
where s.departmentid == 10
select s).ToList();

suppose later if i add more condition like

second line
-------------
student = student.Where(s => s.StudentName == "Jeff");

so tell me what will happen when 2nd line will execute. again a new db trip will occur or filter will occur on whatever data will comes from the first query ?
Nanddeep Nachan8y ago
It is a difference of IEnumerable vs IQueryable.

More comparison here:
https://www.c-sharpcorner.com/UploadFile/a20beb/ienumerable-vs-iqueryable-in-linq/
Sagar Pandurang Kap8y ago
Hi,
Refer from below link :-

https://stackoverflow.com/questions/17968469/whats-the-differences-between-tolist-asenumerable-asqueryable

Hope it helps....