ease vtable declaration using SQLite3::vtable

ext/sqlite3/module.c

@@ -36,6 +36,9 @@ static int xCreate(sqlite3* db, VALUE *module_name,
 	const char* module_name_cstr = (const char*)StringValuePtr(*module_name);
 	const char* table_name_cstr = (const char*)argv[2];
 
+	// method will raise in case of error: no need to use pzErr
+	*pzErr = NULL;
+
 	// lookup for ruby class named like <module_id>::<table_name>
 	module_id = rb_intern( module_name_cstr );
 	module = rb_const_get(rb_cObject, module_id);
@@ -57,8 +60,9 @@ static int xCreate(sqlite3* db, VALUE *module_name,
 		sql_stmt = rb_str_export_to_enc(sql_stmt, rb_utf8_encoding());
 	}
 #endif
-	if ( sqlite3_declare_vtab(db, StringValuePtr(sql_stmt)) )
+	if ( sqlite3_declare_vtab(db, StringValuePtr(sql_stmt)) ) {
 		rb_raise(rb_eArgError, "fail to declare virtual table");
+	}
 
 	return SQLITE_OK;
 }

lib/sqlite3/vtable.rb

@@ -0,0 +1,53 @@
+module SQLite3Vtable
+  # this module contains the vtable classes generated 
+  # using SQLite3::vtable method
+end
+
+module SQLite3
+  class VTableInterface
+    #this method is needed to declare the type of each column to sqlite
+    def create_statement
+      fail 'VTableInterface#create_statement not implemented'
+    end
+
+    #called before each statement
+    def open
+      # do nothing by default
+    end
+
+    #called before each statement
+    def close
+      # do nothing by default
+    end
+
+    # called to retrieve a new row
+    def next
+      fail 'VTableInterface#next not implemented'
+    end
+  end
+
+  def self.vtable(db, table_name, table_columns)
+    if SQLite3Vtable.const_defined?(table_name, inherit = false)
+      raise "'#{table_name}' already declared" 
+    end
+
+    klass = Class.new(VTableInterface) do
+      def initialize(enumerable)
+        @enumerable = enumerable
+      end
+      def create_statement
+        "create table #{table_name}(#{table_columns})"
+      end
+      def next
+        @enumerable.next
+      end
+    end
+
+    begin
+      SQLite3Vtable.const_set(table_name, klass)
+    rescue NameError
+      raise "'#{table_name}' must be a valid ruby constant name"
+    end
+    db.execute("create virtual table #{table_name} using SQLite3Vtable")
+  end
+end

test/test_vtable.rb

@@ -1,8 +1,9 @@
 require "helper"
+require 'sqlite3/vtable'
 
 #the ruby module name should be the one given to sqlite when creating the virtual table.
 module RubyModule
-  class TestVTable
+  class TestVTable < VTableInterface
     def initialize
       @str = "A"*1500
     end
@@ -32,11 +33,6 @@ def next
       end
 
     end
-
-    #required method for vtable
-    #called after each statement
-    def close
-    end
   end
 end