Make all relationships spec fields mandatory

At the moment, we're deciding that if a given relationship doesn't have
a `primary_key`, we fallback to `:id`. This can lead to unwanted behaviour
and suprises from developers.

Let's make it mandatory and ensure everything's present.

Author: oriolgual

lib/resource_registry/relationship_type.rb

@@ -5,6 +5,8 @@ module RelationshipType
     extend T::Sig
     extend T::Helpers
 
+    InvalidRelationshipSpec = Class.new(StandardError)
+
     abstract!
 
     # This enables `is_a?` check type to sorbet
@@ -25,6 +27,7 @@ module RelationshipType
     sig { params(spec: T::Hash[String, T.untyped]).void }
     def initialize(spec)
       @spec = spec
+      validate_spec!
     end
 
     sig { abstract.returns(String) }
@@ -110,7 +113,7 @@ def field
 
     sig { returns(Symbol) }
     def primary_key
-      @spec["primary_key"]&.to_sym || :id
+      @spec["primary_key"]&.to_sym
     end
 
     sig do
@@ -127,5 +130,22 @@ def valid_relationship_field?(read_dto)
     sig { overridable.returns(T.nilable(Symbol)) }
     def relationship_field_name
     end
+
+    private
+
+    sig { void }
+    def validate_spec!
+      errors = []
+      errors << "name is required" unless @spec["name"]
+      errors << "resource_id is required" unless @spec["resource_id"]
+      errors << "field is required" unless @spec["field"]
+      errors << "primary_key is required" unless @spec["primary_key"]
+      errors << "name must be a string" unless @spec["name"].is_a?(String)
+
+      return if errors.empty?
+
+      Kernel.raise InvalidRelationshipSpec,
+                   "The given relationship spec is not valid: #{errors.join(", ")}. The spec is: #{@spec}"
+    end
   end
 end

spec/resource_registry/relationship_spec.rb

@@ -6,21 +6,31 @@
 
 RSpec.describe ResourceRegistry::Relationship do
   describe "#load" do
-    let(:type) { ResourceRegistry::RelationshipTypes::HasOne.new({}) }
     let(:params) do
       {
         "name" => "test",
-        "type" => type.serialize,
+        "type" => "has_one",
         "field" => :test,
         "resource_id" => :test,
-        "optional" => true
+        "optional" => true,
+        "primary_key" => :test
       }
     end
 
     subject { described_class.load(params) }
 
     it { expect(subject).to be_a(described_class) }
 
+    context "when the spec is not valid" do
+      let(:params) { { "type" => "has_one" } }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(
+          ResourceRegistry::RelationshipType::InvalidRelationshipSpec
+        )
+      end
+    end
+
     # TODO: Check how to test this
     xcontext "with a custom type" do
       let(:type) { "policy_resolution" }