Added AsNoTracking for readonly queries

[neyromant]

No description provided.

[LindaLawton]

LGTM

What difference does .AsNoTracking() make?

[neyromant]

@LindaLawton Yes, It avoids the overhead of setting up change tracking for each entity instance. See https://docs.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.entityframeworkqueryableextensions.asnotracking?view=efcore-2.0

[scottbrady91]

This is fine, assuming no one is using these classes and relying on this behavior (which would be weird).

Do you think there will still be a performance improvement given that the dbcontexts are registered as scoped and some of these methods are hit multiple times? I'm wondering if there's a perf decrease for developers not using the store caching.

[neyromant]

@scottbrady91 Note from https://docs.microsoft.com/en-us/ef/core/querying/tracking:

No tracking queries still perform identity resolution within the excuting query. If the result set contains the same entity multiple times, the same instance of the entity class will be returned for each occurrence in the result set. However, weak references are used to keep track of entities that have already been returned. If a previous result with the same identity goes out of scope, and garbage collection runs, you may get a new entity instance. For more information, see How Query Works.

[LindaLawton]

@neyromant very smart i hadnt seen this before. I will be adding it to a few projects.

[neyromant]

I have prepared some simple benchmarks for AsNoTracking (https://github.com/neyromant/Benchmarks/blob/master/Benchmarks/AsNoTracking/AsNoTrackingTests.cs) using BenchmarkDotNet (https://github.com/dotnet/BenchmarkDotNet)

Here is the results:

Method	Records	DbType	Mean	Error	StdDev	Scaled	Gen 0	Gen 1	Gen 2	Allocated
Track	1	InMemory	1,997.5 us	13.308 us	12.448 us	1.00	42.9688	23.4375	7.8125	166.06 KB
NoTrack	1	InMemory	1,766.5 us	10.005 us	8.355 us	0.88	42.9688	21.4844	9.7656	164.92 KB
Track	1	SqlLight	962.1 us	4.921 us	4.362 us	1.00	3.9063	-	-	19.45 KB
NoTrack	1	SqlLight	950.4 us	1.304 us	1.156 us	0.99	3.9063	-	-	18.95 KB
Track	10	InMemory	1,991.6 us	4.890 us	4.574 us	1.00	44.9219	21.4844	9.7656	169.07 KB
NoTrack	10	InMemory	1,835.1 us	3.521 us	3.294 us	0.92	42.9688	21.4844	9.7656	165.53 KB
Track	10	SqlLight	1,011.0 us	2.834 us	2.512 us	1.00	5.8594	-	-	24.33 KB
NoTrack	10	SqlLight	968.5 us	4.634 us	3.870 us	0.96	3.9063	-	-	20.74 KB
Track	100	InMemory	2,195.0 us	7.693 us	7.196 us	1.00	50.7813	27.3438	7.8125	202.41 KB
NoTrack	100	InMemory	1,884.8 us	7.144 us	6.333 us	0.86	42.9688	19.5313	9.7656	166.59 KB
Track	100	SqlLight	1,423.6 us	8.378 us	7.837 us	1.00	17.5781	-	-	74.24 KB
NoTrack	100	SqlLight	1,091.7 us	5.925 us	5.542 us	0.77	7.8125	-	-	38.19 KB
Track	1000	InMemory	4,997.9 us	30.450 us	28.483 us	1.00	101.5625	39.0625	15.6250	534.86 KB
NoTrack	1000	InMemory	1,957.9 us	3.175 us	2.652 us	0.39	42.9688	23.4375	7.8125	173.64 KB
Track	1000	SqlLight	5,880.8 us	43.999 us	41.156 us	1.00	117.1875	39.0625	-	575.44 KB
NoTrack	1000	SqlLight	2,417.2 us	11.036 us	10.323 us	0.41	50.7813	11.7188	-	214.11 KB

[brockallen]

Since we reorganized our repos, I did this change manually. We're tracking here for the release notes: IdentityServer/IdentityServer4#2518.

Thanks!

[neyromant]

So, I will not be on the list of contributors? Well, all right.

[brockallen]

Sorry -- if we hadn't reorganized the repos, then you would have.