Scaffolding: Enable text templates

[bricelam]

This enables users to add T4 templates to their project which will be picked up by dotnet ef dbcontext scaffold to generate the DbContext and entity type classes.

It will look for templates in the following location. Note that the extension .t4 is used instead of the usual .tt so that Visual Studio doesn't try to transform them.

• (Target project directory)
  • CodeTemplates/ (updated in Scaffolding: Use "CodeTemplates" directory #27626)
    • EFCore/
      • DbContext.t4
      • EntityType.t4

Note, I haven't actually written any templates yet--that'll be my next PR. If anyone's eager to start playing with this, the templates would look something like the this: (you'll definitely need to add a few import directives)

<#@ template hostSpecific="true" #>
<#@ parameter name="NamespaceHint" type="System.String" #>
<#@ parameter name="Model" type="Microsoft.EntityFrameworkCore.Metadata.IModel" #>
<#@ parameter name="Options" type="Microsoft.EntityFrameworkCore.Scaffolding.ModelCodeGenerationOptions" #>
<#
    var services = (IServiceProvider)Host;
    var providerCode = services.GetRequiredService<IProviderConfigurationCodeGenerator>();
    var annotationCode = services.GetRequiredService<IAnnotationCodeGenerator>();
    var code = services.GetRequiredService<ICSharpHelper>();
#>
using Microsoft.EntityFrameworkCore;

namespace <#= NamespaceHint #>;

public partial class <#= Options.ContextName #> : DbContext
{
    <# foreach (var entityType in Model.GetEntityTypes()) { #>
    public virtual DbSet<<#= entityType.Name #>> <#= entityType["Scaffolding:DbSetName"] #> { get; set; }
    <# } #>

    protected override void OnConfiguring(DbContextOptionsBuilder options)
        => options<#= code.Fragment(providerCode.GenerateUseProvider(options.ConnectionString)) #>;

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // TODO
    }
}

Part of #4038

To Do

• Use T4 templates when present in the project (this PR)
• Port the existing generators to T4. These will serve as the base templates that users can copy and tweak
• Find a way to distribute the base templates. Either via dotnet new or using a new command in dotnet ef

[ErikEJ]

@bricelam Fantastic!

I plan to add this to Power Tools, so it can drop the files.

A user request I have had in connection with the handlebars templates is the ability supply your own set of "templates", I have enabled this by looking for a .zip file with templates in the project root.

Maybe the to level folder could be called "CodeTemplates" iso "Templates" ?

[ErikEJ]

Maybe use "CodeTemplates" as base folder name?

[bricelam]

Maybe. That’s what it used to be in EF6. I want to run this design by the MVC scaffolding team too and see if they have any future plans. I hinted at this on dotnet/Scaffolding#606 (comment)

[bricelam]

@ErikEJ Do you have any additional reasons for preferring CodeTemplates? (Other than that's what EF6 used.)

[ErikEJ]

It is used by the Handlebars templates. But that is most likely also an EF6 carry over.

[ErikEJ]

Most likely not important. Assume you would never use both and Handlebars could do a breaking change.

[bricelam]

So, I had a crazy idea to generate an ER diagram using mermaid. Here's my template:

<#@ output extension=".md" #>
<#@ assembly name="Microsoft.EntityFrameworkCore" #>
<#@ assembly name="Microsoft.EntityFrameworkCore.Relational" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="Microsoft.EntityFrameworkCore" #>
<#@ import namespace="Microsoft.EntityFrameworkCore.Infrastructure" #>
<#@ import namespace="Microsoft.EntityFrameworkCore.Metadata" #>
<#@ parameter name="Model" type="Microsoft.EntityFrameworkCore.Metadata.IModel" #>
# <#= Model["Scaffolding:DatabaseName"] #>

```mermaid
erDiagram
<#
    foreach (var entityType in Model.GetEntityTypes().Where(t => t.GetViewName() == null && !t.GetForeignKeys().Any(fk => fk.GetReferencingSkipNavigations().Any())))
    {
#>
    <#= entityType.Name.ToUpper() #> {
<#
        foreach (var property in entityType.GetProperties().Where(p => !p.IsForeignKey()))
        {
            var type = property.GetColumnType();
            var lengthStart = type.IndexOf("(");
            if (lengthStart != -1)
                type = type.Substring(0, lengthStart);
#>
        <#= type #> <#= property.Name #>
<#
        }
#>
    }
<#
        foreach (var foreignKey in entityType.GetForeignKeys())
        {
#>
    <#= entityType.Name.ToUpper() #> <#= foreignKey.IsUnique ? "|" : "}" #>o--<#= foreignKey.IsRequired ? "|" : "o" #>| <#= foreignKey.PrincipalEntityType.Name.ToUpper() #> : <#= foreignKey.DependentToPrincipal.Name #>
<#
        }

        foreach (var skipNavigation in entityType.GetSkipNavigations().Where(n => n.JoinEntityType.FindPrimaryKey().Properties[0].GetContainingForeignKeys().First().PrincipalEntityType == entityType))
        {
#>
    <#= entityType.Name.ToUpper() #> }o--o{ <#= skipNavigation.TargetEntityType.Name.ToUpper() #> : <#= skipNavigation.Name #>
<#
        }
    }
#>

And here's what it generates when I point it at Northwind:

Northwind

erDiagram
    CATEGORY {
        int CategoryId
        nvarchar CategoryName
        ntext Description
        image Picture
    }
    CUSTOMER {
        nchar CustomerId
        nvarchar Address
        nvarchar City
        nvarchar CompanyName
        nvarchar ContactName
        nvarchar ContactTitle
        nvarchar Country
        nvarchar Fax
        nvarchar Phone
        nvarchar PostalCode
        nvarchar Region
    }
    CUSTOMER }o--o{ CUSTOMERDEMOGRAPHIC : CustomerTypes
    CUSTOMERDEMOGRAPHIC {
        nchar CustomerTypeId
        ntext CustomerDesc
    }
    EMPLOYEE {
        int EmployeeId
        nvarchar Address
        datetime BirthDate
        nvarchar City
        nvarchar Country
        nvarchar Extension
        nvarchar FirstName
        datetime HireDate
        nvarchar HomePhone
        nvarchar LastName
        ntext Notes
        image Photo
        nvarchar PhotoPath
        nvarchar PostalCode
        nvarchar Region
        nvarchar Title
        nvarchar TitleOfCourtesy
    }
    EMPLOYEE }o--o| EMPLOYEE : ReportsToNavigation
    EMPLOYEE }o--o{ TERRITORY : Territories
    ORDER {
        int OrderId
        money Freight
        datetime OrderDate
        datetime RequiredDate
        nvarchar ShipAddress
        nvarchar ShipCity
        nvarchar ShipCountry
        nvarchar ShipName
        nvarchar ShipPostalCode
        nvarchar ShipRegion
        datetime ShippedDate
    }
    ORDER }o--o| CUSTOMER : Customer
    ORDER }o--o| EMPLOYEE : Employee
    ORDER }o--o| SHIPPER : ShipViaNavigation
    ORDERDETAIL {
        real Discount
        smallint Quantity
        money UnitPrice
    }
    ORDERDETAIL }o--|| ORDER : Order
    ORDERDETAIL }o--|| PRODUCT : Product
    PRODUCT {
        int ProductId
        bit Discontinued
        nvarchar ProductName
        nvarchar QuantityPerUnit
        smallint ReorderLevel
        money UnitPrice
        smallint UnitsInStock
        smallint UnitsOnOrder
    }
    PRODUCT }o--o| CATEGORY : Category
    PRODUCT }o--o| SUPPLIER : Supplier
    REGION {
        int RegionId
        nchar RegionDescription
    }
    SHIPPER {
        int ShipperId
        nvarchar CompanyName
        nvarchar Phone
    }
    SUPPLIER {
        int SupplierId
        nvarchar Address
        nvarchar City
        nvarchar CompanyName
        nvarchar ContactName
        nvarchar ContactTitle
        nvarchar Country
        nvarchar Fax
        ntext HomePage
        nvarchar Phone
        nvarchar PostalCode
        nvarchar Region
    }
    TERRITORY {
        nvarchar TerritoryId
        nchar TerritoryDescription
    }
    TERRITORY }o--|| REGION : Region

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[bricelam]

Tests pass locally on Linux. Not sure why they're timing out on CI...

[AndriySvyryd]

👍

[ghost]

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[ghost]

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[smitpatel]

The concrete class name seems somewhat inconsistent with the interface name

[AraHaan]

Uh this was merged but I do agree, some refinements are needed here.

[ajcvickers]

Just because something has been merged doesn't mean it can't be changed...

[bricelam]

We sure we want to spend our API naming vouchers on internal code?

[smitpatel]

As long as ITextTemplating interface which is public has right name, I am fine whatever the internal concrete type ends up being.

[AndriySvyryd]

The fact that something is Internal doesn't mean it should be of lower quality. We don't review these names because we can change them at any point, not because we don't care

[bricelam]

I take great care in my craft--that's why I chose the names I did. But I'm always happy to hear higher-quality name suggestions.

[AndriySvyryd]

The concrete class name looks good to me, we'll discuss the interface names in API review.

[bricelam]

Agreed. I’ve been thinking of ways we can improve improve things, and I think splitting the class may help. I’ll take a note to discuss it in API review.

P.S. I apologize for my previous comments. They seem out of character and a bit guarded or defensive to me today. I’ll strive for more openness in the future.

[AraHaan]

Add option to inject Code into EntityType templates?

[bricelam]

Use the new, more extensible pattern:

<#@ template hostSpecific="true" #>
<#
    var serviceProvider = (IServiceProvider)Host;
    var code = serviceProvider.GetService<ICSharpHelper>();