Fix enum defined on string columns (#1059)

Fixes
#1042

varchar, varchar_max and text sql server types extends from char
(`ActiveRecord::ConnectionAdapters::SQLServer::Type:Char`).

`ActiveRecord::ConnectionAdapters::SQLServer::Type::Char.serialize` return an `ActiveRecord::ConnectionAdapters::SQLServer::Type::Data` instance.

`Data` defines
```
def eql?(other)
  self.class == other.class && value == other.value
end
```

Let's imagine the following ActiveRecord definition

```
class MyRecord < ActiveRecord::Base
  enum release: { alpha: "A", beta: "B" }
end
```

When we call `my_record.alpha?` it compares `release` serialized value with the
string "A". It will be always false because `Data` and `String` clases
are different.

This commit reimplements `eql?` to deal with string arguments.

Author: mgrunberg

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - [#1052](https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/pull/1052) Ignore casing of VALUES clause when inserting records using SQL
 - [#1053](https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/pull/1053) Fix insertion of records to non-default schema table using raw SQL
+- [#1059](https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/pull/1059) Fix enums defined on string columns
 
 ## v7.0.2.0
 

lib/active_record/connection_adapters/sqlserver/type/data.rb

@@ -27,6 +27,12 @@ def inspect
           end
 
           def eql?(other)
+            # Support comparing `Type::Char`, `Type::Varchar` and `VarcharMax` with strings.
+            # This happens when we use enum with string columns.
+            if other.is_a?(::String)
+              return type.is_a?(ActiveRecord::ConnectionAdapters::SQLServer::Type::String) && value == other
+            end
+
             self.class == other.class && value == other.value
           end
           alias :== :eql?

test/cases/enum_test_sqlserver.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+require "cases/helper_sqlserver"
+
+class EnumTestSQLServer < ActiveRecord::TestCase
+
+  # Check that enums are supported for all string types.
+  # For each type we check: cast, serialize, and update by declaration.
+  # We create a custom class for each type to test.
+  %w[char_10 varchar_50 varchar_max text nchar_10 nvarchar_50 nvarchar_max ntext].each do |col_name|
+    describe "support #{col_name} enums" do
+      let(:klass) do
+        Class.new(ActiveRecord::Base) do
+          self.table_name = 'sst_datatypes'
+
+          enum col_name => { alpha: "A", beta: "B" }
+        end
+      end
+
+      it "type.cast" do
+        type = klass.type_for_attribute(col_name)
+
+        assert_equal "alpha",  type.cast('A')
+        assert_equal "beta",   type.cast('B')
+      end
+
+      it "type.serialize" do
+        type = klass.type_for_attribute(col_name)
+
+        assert_equal 'A', type.serialize('A')
+        assert_equal 'B', type.serialize('B')
+
+        assert_equal 'A', type.serialize(:alpha)
+        assert_equal 'B', type.serialize(:beta)
+      end
+
+      it "update by declaration" do
+        r = klass.new
+
+        r.alpha!
+        assert_predicate r, :alpha?
+
+        r.beta!
+        assert_not_predicate r, :alpha?
+        assert_predicate r, :beta?
+      end
+    end
+  end
+end