Blazor w/ Entity Framework Core - compile error

Question

I have the following setup but am unable to finish building as I get an obscure error related to line 439 in file Blazor.MonoRuntime.targets (MSB3073).

Does this essentially mean that Entity Framework Core will in no way work with Blazor preview 6?

Details:

Asp.net Hosted Blazor

AspNetCore.Blazor (3.0.0-preview6.19307.2)

Microsoft.EntityFrameworkCore (3.0.0-preview6.19304.10)

Microsoft.EntityFrameworkCore.Design (3.0.0-preview6.19304.10)

Microsoft.EntityFrameworkCore.SqlServer (3.0.0-preview6.19304.10)

Resolved via a hack solution!

Somehow I was able to resolve everything and makes things run end-to-end. I believe the big, critical thing was:
* Ensure that the Blazor client AND server projects do not directly reference Entity Framework
* Do not let the Blazor client reference (directly or indirectly) the project with the generated entities). To get access to the models, I just create a duplicate of the generated entities (and removed the "partial" from the classes that were generated)

Are you trying to use EntityFramework from Blazor client-side? If so this is not possible. — Chris Sainty
I want the Blazor server project to communicate with a Data tier project (via API). I generated the EF data context via scaffolding within this Data project. So right now i have the Data project (which has the generated DB Context) and the Server project (which has the EF6 references because scaffolding required it). — AlvinfromDiaspar
Your "hack solution" is really bad. Simply take a look at the Hosted starter template. Of course the server part can use EF. DTO models are a good idea but should not be necessary. — Henk Holterman
I already did. The server part of a Hosted app can and should reference EF. A code-first model is totally independent so it coul be in the Shared part, but better architecture says it shouldn't. A database-fiest model is a little harder to wean of EF, but what you did is sort-of OK. But note that DTO's don't have to be exact copies of the entity classes. Flatten and omit as is needed. — Henk Holterman

enet enet · Accepted Answer · 2019-07-02T17:47:40

Some clarification is needed here, right:

You cannot use Entity Framework on the Client project of Blazor. Entity Framework is a server technology.
You may use Entity Framework on the Server project of your application.
Communication between your Client side and Server hosting side is ordinarily done via Http calls (HttpClient service), but you may also employ SignleR.
To enable Http calls you should expose Http routing endpoints... This can be enabled by using Web Api with the required endpoints. Your Web Api exposed methods (Controllers' methods) can access the database directly (or indirectly if you define repositories, services, etc) via Entity Framework objects, and return the queried data to the calling methods (HttpClient methods).

Note that in my answer I particularly relate to Blazor Client-side apps, but it is mostly true with regards to Blazor server-side apps. I may just add here that in Blazor server-side apps you don't have to use Web Api since Blazor is executed on the server. In such a case, you can define a normal service to retrieve the data from the database, and pass it to the calling methods (no HttpClient involved here).

The Shared project intended to contain objects that can be used by both the front end and back end. This is the place where you can define your Model objects. As for instance, you can define an Employee class that can be used to retrieve the data and pass it to the Client as a list of Employee objects, and in the Client you can define a list of Employee objects that will store the retrieved data. In short, you don't have to define two types of objects, one appropriate to the server, and one appropriate to the client (say your client is an Angular app).

Hope this helps..

Blazor w/ Entity Framework Core - compile error

1 Answers