Introduce has_key? for user context

README.md

@@ -1547,6 +1547,18 @@ schema.with_context(five: 15).(nil)
 # => Datacaster::ValidResult(nil)
 ```
 
+Method `has_key?` could be used to determine whether key is available in the context
+
+```ruby
+schema =
+  Datacaster.schema do
+    check { context.has_key?(:five) }
+  end
+
+schema.with_context(five: 15).(nil)
+# => Datacaster::ValidResult(nil)
+```
+
 **Note**
 
 `context` can be accesed only in casters' blocks. It can't be used in schema definition itself:

lib/datacaster/runtimes/user_context.rb

@@ -4,6 +4,10 @@ module Datacaster
   module Runtimes
     class UserContext < Base
       class ContextStruct
+        def self.context_has_key?(context, key)
+          context.respond_to?(:key?) && context.key?(key) || context.to_h.key?(key.to_sym)
+        end
+
         def initialize(context, node)
           @context = context
           @node = node
@@ -14,10 +18,7 @@ def method_missing(m, *args)
             return super
           end
 
-          key_present = @context.respond_to?(:key?) && @context.key?(m) ||
-            @context.to_h.key?(m.to_sym)
-
-          if key_present && args.empty?
+          if self.class.context_has_key?(@context, m) && args.empty?
             return @context[m]
           end
 
@@ -31,6 +32,12 @@ def method_missing(m, *args)
             raise NoMethodError.new("Key #{m.inspect} is not found in the context")
           end
         end
+
+        def has_key?(key)
+          self.class.context_has_key?(@context, key) || @node.class.send_to_parent(@node, :context).has_key?(key)
+        rescue NoMethodError
+          false
+        end
       end
 
       def initialize(parent, user_context)

lib/datacaster/version.rb

@@ -1,3 +1,3 @@
 module Datacaster
-  VERSION = "4.0.1"
+  VERSION = "4.1.0"
 end

spec/user_context_spec.rb

@@ -79,4 +79,29 @@
       expect(schema.with_context(d: 2, e: 3).({a: 1, b: {c: {d: 10}}, e: [3]}).to_dry_result).to eq Failure({b: {c: {d: ["is invalid"]}}})
     end
   end
+
+  describe "using #has_key?" do
+    it "works with deep nesting" do
+      schema = described_class.schema do
+        check { context.has_key?(:b) && context.has_key?(:c) && context.has_key?(:d) && !context.has_key?(:e) }.
+          with_context(b: 1).
+          with_context(c: 2).
+          with_context(d: 3)
+      end
+
+      expect(schema.with_context(a: 1).(1).to_dry_result).to eq Success(1)
+    end
+
+    it "works with complex schemas" do
+      schema = described_class.schema do
+        hash_schema(
+          a: check { context.has_key?(:a) && context.has_key?(:d) && context.has_key?(:e) && !context.has_key?(:f) },
+          b: {c: {d: check { context.has_key?(:a) && context.has_key?(:d) && context.has_key?(:e) && !context.has_key?(:t) }}},
+          e: [check { |v| context.has_key?(:a) && context.has_key?(:d) && context.has_key?(:e) && !context.has_key?(:p) }]
+        ).with_context(a: 1)
+      end
+
+      expect(schema.with_context(d: 2, e: 3).({a: 1, b: {c: {d: 10}}, e: [3]}).to_dry_result).to eq Success({:a=>1, :b=>{:c=>{:d=>10}}, :e=>[3]})
+    end
+  end
 end