Add child logger with instance named tags support

CHANGELOG.md

@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [unreleased]
 
+- Add child logger with instance named tags support
+
 ## [4.17.0]
 
 - Correct `source_code_uri` URL

docs/api.md

@@ -633,4 +633,18 @@ Or, when using a Gemfile:
 gem "semantic_logger", require: "semantic_logger/sync"
 ~~~
 
+### Child Logger
+
+It is possible to create child loggers with pre-set instance tags.
+Any log message emitted by a logger with pre-set instance tags will include these tags along with the message data.
+
+~~~ruby
+logger = SemanticLogger["MyClass"]
+child_logger1 = logger.child(tag1: "value1", tag2: "value2")
+child_logger2 = child_logger1.child(tag3: "value3")
+
+# Will include tag1, tag2, tag3 and tag4 in the output
+child_logger2.info("Some message", tag4: "value4")
+~~~
+
 ### [Next: Testing ==>](testing.html)

lib/semantic_logger/base.rb

@@ -7,7 +7,7 @@
 module SemanticLogger
   class Base
     # Class name to be logged
-    attr_accessor :name, :filter
+    attr_accessor :name, :filter, :child_named_tags
 
     # Set the logging level for this logger
     #
@@ -250,6 +250,14 @@ def should_log?(log)
       meets_log_level?(log) && !filtered?(log)
     end
 
+    # Creates a new logger with the given instance named tags
+    def child(**named_tags)
+      new_named_tags = child_named_tags.merge(named_tags)
+      new_logger = dup
+      new_logger.child_named_tags = new_named_tags
+      new_logger
+    end
+
     private
 
     # Initializer for Abstract Class SemanticLogger::Base
@@ -290,6 +298,7 @@ def initialize(klass, level = nil, filter = nil)
       else
         self.level = level
       end
+      @child_named_tags = {}
     end
 
     # Return the level index for fast comparisons
@@ -349,6 +358,9 @@ def log_internal(level, index, message = nil, payload = nil, exception = nil)
         end
       end
 
+      # Add child named tags to the log
+      log.payload = child_named_tags.merge(log.payload || {})
+
       # Log level may change during assign due to :on_exception_level
       self.log(log) if should_log && should_log?(log)
     end
@@ -389,6 +401,9 @@ def measure_internal(level, index, message, params)
         # Extract options after block completes so that block can modify any of the options
         payload = params[:payload]
 
+        # Add child named tags
+        payload = child_named_tags.merge(payload || {})
+
         # May return false due to elastic logging
         should_log = log.assign(
           message:            message,

lib/semantic_logger/loggable.rb

@@ -42,7 +42,7 @@ def self.included(base)
 
         # Returns [SemanticLogger::Logger] class level logger
         def self.logger
-          @semantic_logger ||= SemanticLogger[self]
+          @semantic_logger ||= SemanticLogger[self].child(**@logger_child_named_tags)
         end
 
         # Replace instance class level logger
@@ -114,6 +114,10 @@ def #{method_name}(*args, &block)
         true
       end
 
+      def logger_child(**named_tags)
+        @logger_child_named_tags = named_tags
+      end
+
       private
 
       # Dynamic Module to intercept method calls for measuring purposes.

test/loggable_test.rb

@@ -27,6 +27,14 @@ class TestAttribute
     include SemanticLogger::Loggable
   end
 
+  class TestChildClassLogger
+    include SemanticLogger::Loggable
+
+    TAG_DATA = {tag1: "value1", tag2: "value2"}.freeze
+
+    logger_child(**TAG_DATA)
+  end
+
   describe SemanticLogger::Loggable do
     describe "inheritance" do
       it "should give child classes their own logger" do
@@ -79,5 +87,11 @@ class TestAttribute
         TestAttribute.new.logger.is_a?(SemanticLogger::Logger)
       end
     end
+
+    describe "sample child class logger" do
+      it "has child named tags set" do
+        assert_equal TestChildClassLogger::TAG_DATA, TestChildClassLogger.logger.child_named_tags
+      end
+    end
   end
 end

test/logger_test.rb

@@ -153,5 +153,18 @@ def self.call(log)
         end
       end
     end
+
+    describe ".child" do
+      it "creates a child logger" do
+        tag_data = {tag1: "value1", tag2: "value2"}
+        child_logger = logger.child(**tag_data)
+        child_logger.info("hello world")
+
+        assert_equal tag_data, child_logger.child_named_tags
+        assert log = child_logger.events.first
+        assert_equal "hello world", log.message
+        assert_equal tag_data, log.payload
+      end
+    end
   end
 end