feat: Omit Columns from SQL statements (e.g uuid columns)

I've added two options for omitting columns from the SQL statements, to avoid having to modify class level `self.ignored_columns` since we've had issues with this affecting other code that runs at the same time. These options work as follows:

`Model.import(values, omit_columns: [:guid])` # Omit the guid column from SQL statement, allowing it to generate
`Model.import(values, omit_columns: -> (model, column_name) { [:guid] if model == Model })` Allow per-model decisions, e.g for recursive imports
`Model.import(values, omit_columns: { Model => [:guid] })` Use a hash instead of a proc

The second option is `:omit_columns_with_default_functions` boolean, to automatically find columns that have a default function declared in the schema, and omit them by default.

fix: Require AR 5.0+

README.markdown

@@ -30,31 +30,36 @@ The gem provides the following high-level features:
 
 ## Table of Contents
 
-* [Examples](#examples)
-  * [Introduction](#introduction)
-  * [Columns and Arrays](#columns-and-arrays)
-  * [Hashes](#hashes)
-  * [ActiveRecord Models](#activerecord-models)
-  * [Batching](#batching)
-  * [Recursive](#recursive)
-* [Options](#options)
-  * [Duplicate Key Ignore](#duplicate-key-ignore)
-  * [Duplicate Key Update](#duplicate-key-update)
-* [Return Info](#return-info)
-* [Counter Cache](#counter-cache)
-* [ActiveRecord Timestamps](#activerecord-timestamps)
-* [Callbacks](#callbacks)
-* [Supported Adapters](#supported-adapters)
-* [Additional Adapters](#additional-adapters)
-* [Requiring](#requiring)
-  * [Autoloading via Bundler](#autoloading-via-bundler)
-  * [Manually Loading](#manually-loading)
-* [Load Path Setup](#load-path-setup)
-* [Conflicts With Other Gems](#conflicts-with-other-gems)
-* [More Information](#more-information)
-* [Contributing](#contributing)
-  * [Running Tests](#running-tests)
-  * [Issue Triage](#issue-triage)
+- [Activerecord-Import ](#activerecord-import-)
+  - [Table of Contents](#table-of-contents)
+    - [Examples](#examples)
+      - [Introduction](#introduction)
+      - [Columns and Arrays](#columns-and-arrays)
+      - [Hashes](#hashes)
+      - [Import Using Hashes and Explicit Column Names](#import-using-hashes-and-explicit-column-names)
+      - [ActiveRecord Models](#activerecord-models)
+      - [Batching](#batching)
+      - [Recursive](#recursive)
+    - [Options](#options)
+      - [Duplicate Key Ignore](#duplicate-key-ignore)
+      - [Duplicate Key Update](#duplicate-key-update)
+    - [Return Info](#return-info)
+    - [Counter Cache](#counter-cache)
+    - [ActiveRecord Timestamps](#activerecord-timestamps)
+    - [Callbacks](#callbacks)
+    - [Supported Adapters](#supported-adapters)
+    - [Additional Adapters](#additional-adapters)
+    - [Requiring](#requiring)
+      - [Autoloading via Bundler](#autoloading-via-bundler)
+      - [Manually Loading](#manually-loading)
+    - [Load Path Setup](#load-path-setup)
+    - [Conflicts With Other Gems](#conflicts-with-other-gems)
+    - [More Information](#more-information)
+    - [Contributing](#contributing)
+      - [Running Tests](#running-tests)
+  - [Issue Triage ](#issue-triage-)
+- [License](#license)
+- [Author](#author)
 
 ### Examples
 
@@ -277,6 +282,8 @@ Key                       | Options               | Default            | Descrip
 :batch_size               | `Integer`             | total # of records | Max number of records to insert per import
 :raise_error              | `true`/`false`        | `false`            | Raises an exception at the first invalid record. This means there will not be a result object returned. The `import!` method is a shortcut for this.
 :all_or_none              | `true`/`false`        | `false`            | Will not import any records if there is a record with validation errors.
+:omit_columns             | `Array`/`Hash`/`Proc` | `nil`              | Array of columns to leave out of SQL statement, e.g `[:guid]`, or Hash of `{ Model => [:column_name] }` or a Proc `-> (model, column_names) { [:guid] }` returning columns to omit
+:omit_columns_with_default_functions | `true` / `false` | `false`      | Automatically omit columns that have a default function defined in the schema, such as non-PK uuid columns
 
 #### Duplicate Key Ignore
 

lib/activerecord-import/import.rb

@@ -351,6 +351,13 @@ def supports_setting_primary_key_of_imported_objects?
     #   newly imported objects. PostgreSQL only.
     # * +batch_size+ - an integer value to specify the max number of records to
     #   include per insert. Defaults to the total number of records to import.
+    # * +omit_columns+ an array of column names to exclude from the import,
+    #   or a proc that receives the class, and array of column names, and returns
+    #   a new array of column names (for recursive imports). This is to avoid
+    #   having to populate Model.ignored_columns, which can leak to other threads.
+    # * +omit_columns_with_default_functions+ - true|false, tells import to filter
+    #   out all columns with a default function defined in the schema, such as uuid
+    #   columns that have a default value of uuid_generate_v4(). Defaults to false.
     #
     # == Examples
     #  class BlogPost < ActiveRecord::Base ; end
@@ -552,9 +559,60 @@ def bulk_import!(*args)
     end
     alias import! bulk_import! unless ActiveRecord::Base.respond_to? :import!
 
+    # Filters column names for a model according to the options given,
+    # specifically the :omit_columns and :omit_columns_with_default_functions options
+    def omitted_column_names(column_names, options)
+      model = options[:model]
+      # binding.pry if model == Redirection
+      ignored_column_names = []
+
+      # Do nothing if none of these options are truthy
+      return ignored_column_names unless options.slice(:omit_columns, :omit_columns_with_default_functions).values.any?
+
+      # Remove columns that have default functions defined if the option is given
+      ignored_column_names += columns_with_default_function.map(&:name).map(&:to_sym) if options[:omit_columns_with_default_functions]
+
+      if (omit_columns = options[:omit_columns])
+        # If the option is a Proc, which is useful for recursive imports
+        # where the model class is not known yet, call it with the model
+        # and the current set of column names and expect it to return
+        # columns to ignore
+        # Cast to array in case it returns a falsy value
+        case omit_columns
+        when Proc
+          ignored_column_names += Array(omit_columns.call(model, column_names)).map(&:to_sym)
+        when Array
+          ignored_column_names += omit_columns.map(&:to_sym)
+        when Hash
+          # ignore_columns could also be a hash of { Model => [:guid, :uuid], OtherModel => [:some_column] }
+          ignored_column_names += Array(omit_columns[model]).map(&:to_sym) if omit_columns[model]
+        end
+      end
+      ignored_column_names
+    end
+
+    # Finds all columns that have a default function defined
+    # in the schema. These columns should not be forcibly set
+    # to NULL even if it's allowed.
+    # If options[:omit_columns_with_default_functions] is given,
+    # we use this list to remove these columns from the list and
+    # subsequently from the schema column hash.
+    def columns_with_default_function
+      columns.select do |column|
+        # We should probably not ignore the primary key?
+        # If we should, it's not the job of this method to do so,
+        # so don't return the primary key in this list.
+        next if column.name == primary_key
+        # Any columns that have a default function
+        next unless column.default_function
+        true
+      end
+    end
+
     def import_helper( *args )
       options = { model: self, validate: true, timestamps: true, track_validation_failures: false }
       options.merge!( args.pop ) if args.last.is_a? Hash
+
       # making sure that current model's primary key is used
       options[:primary_key] = primary_key
       options[:locking_column] = locking_column if attribute_names.include?(locking_column)
@@ -576,6 +634,9 @@ def import_helper( *args )
           end
         end
 
+        # Filter column names according to the options given
+        # before proceeding to construct the array of attributes
+        column_names -= omitted_column_names(column_names, options).map(&:to_s)
         if models.first.id.nil?
           Array(primary_key).each do |c|
             if column_names.include?(c) && schema_columns_hash[c].type == :uuid
@@ -626,15 +687,22 @@ def import_helper( *args )
           allow_extra_hash_keys = false
         end
 
+        # When importing an array of hashes, we know `self` is the current model
+        omitted_column_names = omitted_column_names(column_names, options)
+
         array_of_attributes = array_of_hashes.map do |h|
           error_message = validate_hash_import(h, column_names, allow_extra_hash_keys)
 
           raise ArgumentError, error_message if error_message
 
-          column_names.map do |key|
+          # Ensure column attributes are set to the filtered list after validation,
+          # but validate as if the original list was passed in so that we dont
+          # fail validation on columns that are going to be ignored
+          (column_names - omitted_column_names).map do |key|
             h[key]
           end
         end
+
         # supports empty array
       elsif args.last.is_a?( Array ) && args.last.empty?
         return ActiveRecord::Import::Result.new([], 0, [], [])
@@ -657,6 +725,10 @@ def import_helper( *args )
       # Force the primary key col into the insert if it's not
       # on the list and we are using a sequence and stuff a nil
       # value for it into each row so the sequencer will fire later
+
+      # Remove omitted columns
+      column_names -= omitted_column_names(column_names, options)
+
       symbolized_column_names = Array(column_names).map(&:to_sym)
       symbolized_primary_key = Array(primary_key).map(&:to_sym)
 

test/models/redirection.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class Redirection < ActiveRecord::Base
+end

test/schema/postgresql_schema.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 ActiveRecord::Schema.define do
+  enable_extension "pgcrypto"
   execute('CREATE extension IF NOT EXISTS "hstore";')
   execute('CREATE extension IF NOT EXISTS "pgcrypto";')
   execute('CREATE extension IF NOT EXISTS "uuid-ossp";')
@@ -56,5 +57,16 @@
     t.datetime :updated_at
   end
 
+  create_table :redirections, force: :cascade do |t|
+    t.uuid "guid", default: -> { "gen_random_uuid()" }
+    t.string :title, null: false
+    t.string :author_name
+    t.string :url
+    t.datetime :created_at
+    t.datetime :created_on
+    t.datetime :updated_at
+    t.datetime :updated_on
+  end
+
   add_index :alarms, [:device_id, :alarm_type], unique: true, where: 'status <> 0'
 end