Add table_without_primary_key checker

README.md

@@ -15,6 +15,7 @@ can detect:
 * incorrect values of `dependent` on associations - [`active_record_doctor:incorrect_dependent_option`](#detecting-incorrect-dependent-option-on-associations)
 * primary keys having short integer types - [`active_record_doctor:short_primary_key_type`](#detecting-primary-keys-having-short-integer-types)
 * mismatched foreign key types - [`active_record_doctor:mismatched_foreign_key_type`](#detecting-mismatched-foreign-key-types)
+* tables without primary keys - [`active_record_doctor:table_without_primary_key`](#detecting-tables-without-primary-keys)
 
 It can also:
 
@@ -602,6 +603,29 @@ Supported configuration options:
 - `ignore_columns` - foreign keys, written as table.column, that should not be
   checked.
 
+### Detecting Tables Without Primary Keys
+
+Tables should have primary keys. Otherwise, it becomes problematic to easily find a specific record,
+logical replication in PostgreSQL will be troublesome, because all the rows need to be unique
+in the table then etc.
+
+Running the command below will list all tables without primary keys:
+
+```
+bundle exec rake active_record_doctor:table_without_primary_key
+```
+
+The output of the command looks like this:
+
+```
+add a primary key to companies
+```
+
+Supported configuration options:
+
+- `enabled` - set to `false` to disable the detector altogether
+- `ignore_tables` - tables whose primary key existense should not be checked
+
 ## Ruby and Rails Compatibility Policy
 
 The goal of the policy is to ensure proper functioning in reasonable

lib/active_record_doctor.rb

@@ -20,6 +20,7 @@
 require "active_record_doctor/detectors/incorrect_dependent_option"
 require "active_record_doctor/detectors/short_primary_key_type"
 require "active_record_doctor/detectors/mismatched_foreign_key_type"
+require "active_record_doctor/detectors/table_without_primary_key"
 require "active_record_doctor/errors"
 require "active_record_doctor/help"
 require "active_record_doctor/runner"

lib/active_record_doctor/config/default.rb

@@ -58,6 +58,10 @@
     enabled: true,
     ignore_tables: []
 
+  detector :table_without_primary_key,
+    enabled: true,
+    ignore_tables: []
+
   detector :undefined_table_references,
     enabled: true,
     ignore_models: []

lib/active_record_doctor/detectors/table_without_primary_key.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require "active_record_doctor/detectors/base"
+
+module ActiveRecordDoctor
+  module Detectors
+    class TableWithoutPrimaryKey < Base # :nodoc:
+      @description = "detect tables without primary keys"
+      @config = {
+        ignore_tables: {
+          description: "tables whose primary key existense should not be checked",
+          global: true
+        }
+      }
+
+      private
+
+      def message(table:)
+        "add a primary key to #{table}"
+      end
+
+      def detect
+        each_table(except: config(:ignore_tables)) do |table|
+          column = primary_key(table)
+          problem!(table: table) unless column
+        end
+      end
+    end
+  end
+end

test/active_record_doctor/detectors/table_without_primary_key_test.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class ActiveRecordDoctor::Detectors::TableWithoutPrimaryKeyTest < Minitest::Test
+  def test_table_without_primary_key_reported
+    Context.create_table(:companies, id: false) do |t|
+      t.string :name
+    end
+
+    assert_problems(<<~OUTPUT)
+      add a primary key to companies
+    OUTPUT
+  end
+
+  def test_table_with_primary_key_is_not_reported
+    Context.create_table(:companies)
+    refute_problems
+  end
+
+  def test_config_ignore_tables
+    Context.create_table(:companies, id: false) do |t|
+      t.string :name
+    end
+
+    config_file(<<-CONFIG)
+      ActiveRecordDoctor.configure do |config|
+        config.detector :table_without_primary_key,
+          ignore_tables: ["companies"]
+      end
+    CONFIG
+
+    refute_problems
+  end
+
+  def test_global_ignore_tables
+    Context.create_table(:companies, id: false) do |t|
+      t.string :name
+    end
+
+    config_file(<<-CONFIG)
+      ActiveRecordDoctor.configure do |config|
+        config.global :ignore_tables, ["companies"]
+      end
+    CONFIG
+
+    refute_problems
+  end
+end