Blazor - Scaffold-DBContext issues?

Question

User379720387 posted

I am using this tutorial to educate myself on Blazor

Scaffold-DBContext seems pretty straightforward to set up:

First, we will install the package for the database provider that we are targeting which is SQL Server in this case. Hence, run the following command:

Install-Package Microsoft.EntityFrameworkCore.SqlServer

Since we are using Entity Framework Tools to create a model from the existing database, we will install the tools package as well. Hence, run the following command:

Install-Package Microsoft.EntityFrameworkCore.Tools

After you have installed both the packages, we will scaffold our model from the database tables using the following command:

Scaffold-DbContext "Your connection string here" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models -Tables Employee, Cities

Do not forget to put your own connection string (inside  " "). After this command gets executed successfully you can observe a Models folder has been created inside ServerSideSPA.App project and it contains three class files myTestDBContext.cs, Cities.cs, and Employee.cs. Hence, we have successfully scaffolded our Models using EF core database first approach.

I did get the Models folder and the 3 class files, but I don't think I actually have a connection to the db, so I am wondering about "your connection string here"

Then I found the  learnentityframeworkcore.com walkthrough for an existing database here

If you are working with Visual Studio, you can use the Package Manager Console commands to generate the the code files for the model. The equivalent command to the last CLI command just above is:

1. PM> Scaffold-DbContext "Server=.\;Database=AdventureWorksLT2012;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Model -Context "AdventureContext" -DataAnnotations

I took that as (Package Manager console):

"Server=S4000W\SQLSERVER;Database=BLZR;Trusted_Connection=True;"

Now I am wondering if the Models folder and classes got created without actually connecting to my db?

Answer 1

User1120430333 posted

Why don't you just delete the whole project and start over, a simple approach? 

Answer 2

User379720387 posted

yes, that is the plan.

Right now I don't have any other information than what I tried first.  My expectation would be the same outcome.

Any thoughts on the connection string?

Answer 3

User-821857111 posted

You need to specify a connection string for the tooling to use so that it can examine the database schema and generate the appropriate model files. So I don;t know how your first attempt worked unless you supplied a connection string.

The connection string is a standard database connection string. What you posted looks valid.

Answer 4

User379720387 posted

I did use this:

Scaffold-DbContext "Server=S4000W\SQLSERVER;Database=BLZR;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models -Tables Employee, Cities

It created the DBContext, but I don't think there was an actual connection to the db.

Answer 5

User-821857111 posted

Why don't think a connection was made to the database?

Answer 6

User379720387 posted

It wasn't loading the data that is in the db.

Answer 7

User-821857111 posted

The scaffolding process doesn't query data. The data itself has no value in the process. It queries the database schema. It constructs the model files from the schema.

Answer 8

User379720387 posted

I realize that.

The three model class files were created

All the code is there to show the Employee records. Nothing came up, that is why I am considering if model files can be created without having a connection to the db.

Answer 9

User-1764593085 posted

Hi wavemaster,

If you have correct Server name, there seems no problem with your connection string.You could refer to EF core Db first tutorial to do that with localdb.

Make sure seed data to your Employee table in database. Then you could also check your code to the source code of your blazor tutorial to find the differences.

Xing

Answer 10

User-821857111 posted

wavemaster

All the code is there to show the Employee records. Nothing came up

Probably my bad, but I'm struggling to follow. Where is all the code to show the Employee record? Where do you expect the data to "come up"? I'm unclear where in the process you expected data to appear and why you expect it. 

Answer 11

User379720387 posted

I am following this tutorial here:

https://dzone.com/articles/single-page-application-using-server-side-blazor-a

Towards the bottom "EXECUTION DEMO" and the fetchemployee part.

I added an Employee record directly in the db.

Should have come up on the fetchemployee page.

Answer 12

User-821857111 posted

I'm unclear what that has to do with scaffolding.

Answer 13

User379720387 posted

My question is this.... can I be sure that when the scaffolding succeeds and creates the model class that I have access to the db?

Don't know enough to test for myself that there is a connection to the db.

Answer 14

User475983607 posted

My question is this.... can I be sure that when the scaffolding succeeds and creates the model class that I have access to the db?

The command had to open and connect to the database to read the table schemas and create the DbContext and Entities as explained above.  

Maybe, the connection used to scaffold the DB is not the same DB used to add records.

Answer 15

User-821857111 posted

My question is this.... can I be sure that when the scaffolding succeeds and creates the model class that I have access to the db?

Don't know enough to test for myself that there is a connection to the db.

Yes. The production of the model class files is evidence that the tooling successfully connected to the database. The reverse engineering process cannot success without connecting to the database. 

You can use SQL Server Profiler to see the commands being executed against your database: https://docs.microsoft.com/en-us/sql/tools/sql-server-profiler/start-sql-server-profiler?view=sql-server-2017