iOS cannot save Entity models with Nullable Guid (Guid?) property types (among others) using EF Core 2.1.2.

[cfdelaune]

Steps to Reproduce

1. Download, extract, and load the sample solution in Visual Studio 15.8.1.
   iOSEFCore212.zip

2. Build and run the project, targeting a physical iPhone device.

PLEASE NOTE: This project has been adapted from the sample provided by @cwrea for a preceding issue described here.

Expected Behavior

The project should build and run, writing some lines to debug output indicating that Entity Framework Core has created a database from the simple model included in the project, saved a few test records, and retrieved them.

Actual Behavior

The following exception is encountered when AddAsync() is called against the DbSet:

System.ExecutionEngineException: Attempting to JIT compile method '(wrapper runtime-invoke) <Module>:runtime_invoke_void__this___int_byte_object_object_DateTime_Nullable1<DateTime>_Decimal_Guid_Nullable1<Guid>_Nullable1<int> (object,intptr,intptr,intptr)' while running in aot-only mode. See https://developer.xamarin.com/guides/ios/advanced_topics/limitations/ for more information. occurred

If the model (TodoItem.cs) does not contain a property of type Guid?, the project works without issue. Note that DateTime?, int?, and bool? property types work, but a similar error will be encountered for the decimal? type. I have not tested any additional nullable types at this time.

This issue is similar to https://bugzilla.xamarin.com/show_bug.cgi?id=58424 and https://bugzilla.xamarin.com/show_bug.cgi?id=59184, both of which have been marked as RESOLVED FIXED. I have submitted this per the suggestion of @divega.

Environment

Microsoft Visual Studio Professional 2017 
Version 15.8.1
VisualStudio.15.Release/15.8.1+28010.2003
Microsoft .NET Framework
Version 4.7.03056

Installed Version: Professional

ActiveReports 11   11.2.12190.0
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ASP.NET Web Frameworks and Tools 2017   5.2.60618.0
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Azure App Service Tools v3.0.0   15.8.05023.0
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Azure Data Lake Node   1.0
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Azure Data Lake Tools for Visual Studio   2.3.4000.4
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Fabric.DiagnosticEvents   1.0
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Merq   1.1.38 (5b3c069)
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Microsoft Azure Hive Query Language Service   2.3.4000.4
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Microsoft Azure Stream Analytics Node   1.0
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Microsoft Azure Tools   2.9
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Microsoft Continuous Delivery Tools for Visual Studio   0.4
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Microsoft JVM Debugger   1.0
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Microsoft Library Manager   1.0
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Microsoft MI-Based Debugger   1.0
Provides support for connecting Visual Studio to MI compatible debuggers

Microsoft Visual Studio Tools for Containers   1.1
Develop, run, validate your ASP.NET Core applications in the target environment. F5 your application directly into a container with debugging, or CTRL + F5 to edit & refresh your app without having to rebuild the container.

Mono Debugging for Visual Studio   4.11.7-pre (8955b2a)
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NuGet Package Manager   4.6.0
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ProjectServicesPackage Extension   1.0
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ResourcePackage Extension   1.0
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SQL Server Data Tools   15.1.61808.07020
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Visual Basic Tools   2.9.0-beta8-63208-01
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Visual F# Tools 10.2 for F# 4.5   15.8.0.0.  Commit Hash: c55dd2c3d618eb93a8d16e503947342b1fa93556.
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Visual Studio Code Debug Adapter Host Package   1.0
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Visual Studio Spell Check Everywhere   VSSpellCheckEverywhere
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https://github.com/EWSoftware/VSSpellChecker

Visual Studio Tools for Containers   1.0
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VisualStudio.Mac   1.0
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Xamarin   4.11.0.732 (d15-8@33e83e124)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.

Xamarin Designer   4.14.218 (79f535bdd)
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Xamarin Templates   1.1.113 (e1d02a7)
Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms.

Xamarin.Android SDK   9.0.0.18 (HEAD/3d8a28f1a)
Xamarin.Android Reference Assemblies and MSBuild support.

Xamarin.iOS and Xamarin.Mac SDK   11.14.0.13 (373c313)
Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support.

Build Logs

The project builds without issue.

Example Project (If Possible)

iOSEFCore212.zip

[mauruskuehne]

We have this problem too in our app. @cfdelaune do you have a workaround for this until it's fixed?

[cfdelaune]

Unfortunately, no. I have been fighting with this problem for months. Until VS 2017 15.7.6, I could not even compile, so I am just now able to identify the specific problem.

[ysmoradi]

The workaround is here! https://github.com/ysmoradi/EfCoreiOSIssue/
@cfdelaune @mauruskuehne @cwrea @1saeedsalehi

[divega]

@rolfbjarne can you please provide more information about what specific limitation in Xamarin iOS this is hitting?

Also, any chance this can be re-prioritized? We have been getting lots of feedback from Xamarin customers trying to use EF Core and we have been working through issues with several people in the Xamarin team, trying to get things to a place in which we can claim it is usable and a good experience.

And it seems we are getting so close! But having something like this lingering in the "Future" milestone could cause a lot of pain.

[ysmoradi]

@divega I've used ef core in many xamarin based projects. I've experienced 3 pains. 1- Poor performance on android devices, 2- sqlite migrations limitations and this issue. You're generating code at runtime using lambda expressions (NewExpression + Compile), and this violates iOS limitations. You may not generate code at runtime in iOS apps. I think you've used that feature to improve overall performance in some scenarios. Xamarin iOS has some workarounds for code generations at runtime and not every code generation results into exception. But when you talk about generics (Nullable for example), you can encounter a problem far easier!

[mandel-macaque]

Here is some extra information. I have been able to reproduce the bug with Xamarin.iOS 11.14.0.13 (373c313), which is the one used to report the issue. I have also tested the following environments:

-Latests stable Wit a successful build which is successful when running the application on a device it crashes.

-Beta channel Similar build success.

-Alpha channel The build fails with an unrelated issue.

-Xcode 10 branch Application also builds with no errors And like the others, app crashes.

[rolfbjarne]

@ysmoradi I'm not sure which limitation this is hitting, it might just be a bug too. I'll have to forward this to the mono team for them to have a look at it.

[rolfbjarne]

This issue was moved to mono/mono#10483