You can easily add your own compile-time check via method generators. Here's an example which checks that all abastract methods are implemented.

Class Test.AbstractChecker
{

ClassMethod Check() As %Status [ CodeMode = objectgenerator, ForceGenerate ]
{
    #Dim sc As %Status = $$$OK
    
    // Get class name from %compiledclass object which is an instance of a currently compiled class
    Set class = %compiledclass.Name

    // Iterate over class methods.
    // You can also use %class object to iterate
    Set method=$$$comMemberNext(class, $$$cCLASSmethod, "")
    While method'="" {
        
        // Get mthod abstract state
        Set abstract = $$$comMemberKeyGet(class, $$$cCLASSmethod, method, $$$cMETHabstract)
        
        // Quit iteration when we find any abstract compiled method
        If abstract {
            set origin = $$$comMemberKeyGet(class, $$$cCLASSmethod, method, $$$cMETHorigin)
            Set sc = $$$ERROR($$$GeneralError, $$$FormatText("Abstract method %1 in class %2 not implemented (origins from %3)", method, class, origin))
            Quit
        }
        
        // Get next method
        Set method=$$$comMemberNext(class, $$$cCLASSmethod, method)        
    }
    Quit sc
}

}

After adding this class to inheritance I get an error on compilation:

DataGrip works.

How do I reference parent from child if parent id is composite?

Here's my global:

^data("idA", "idB") = "Parent"
^data("idA", "idB", 1) = "Child"

And Class is:

Class Parent {
Property IdAProp;
Property IdBProp;
}

SQL Storage for Parent works.

For Child I have tried:

<Subscript name="1">
<Expression>{User.Parent.IdAProp}</Expression>
</Subscript>
<Subscript name="2">
<Expression>{User.Parent.IdBProp}</Expression>
</Subscript>
<Subscript name="3">
<Expression>{Position}</Expression>
</Subscript>

But compilation fails with:

ERROR #5547: Map: Map1 - Subscript Expression - invalid expression '{User.Parent.IdAProp}'.  Must be a valid field reference.    If this is the Master Map, it must be an IDKEY field.
  > ERROR #5030: An error occurred while compiling class 'User.Children'

UPD. SQL schema name should be used, not class.

Class SerialA Extends (%SerialObject, %XML.Adaptor) [ ProcedureBlock ]
{
      Property SerialB as SerialB;
     Property SerialC as SerialC(XMLPROJECTION = "NONE");
}

I'm creating a new SQL storage:

However I don't have "Next" button enabled. And if I press "Finish" I exit the WIzard.

How do I get to this screen?

Calling @Bob Kuszewski 
 

User needs USE permissions on the %Ens_MessageHeader resource to view Message Viewer page.

You can add custom role granting Use on the resource or add %EnsRole_Operator role to the user (note that it does add a lot more).

You can see it in the Management Portal:

Any particular reason you want to use DocDB and not relational tables?

Send http request to get the feed and %XML.Reader to parse it into individual objects.

Use BS/BO to automate sending http requests.

Please add a code sample to demonstrate your issue.

Here's my simple class:

Class test.json Extends (%RegisteredObject, %JSON.Adaptor)
{

Property int As %Integer [ InitialExpression = 4 ];

/// do ##class(test.json).test()
ClassMethod test()
{
    set obj = ..%New()
    set sc = obj.%JSONExport()
}

}

And in the terminal I get the expected output:

do ##class(test.json).test()
{"int":4}

To know how a particular DTL action translates into ObjectScript:

1. Open DTL class in Studio
2. Press Ctrl+Shift+V OR See Other Code Button
3. Check Transform method - it contains ObjectScript implementation for the DTL

Compiler does build dependency tree. If you encounter some kind of the issue where your classes are not compiled in a correct order you might open a WRC ticket.

Use DependsOn keyword to provide hints to compiler.