Module: N::DbTools

Defined in:
lib/n/db/tools.rb

Overview

DbConnection

A Connection to the Database.

Class Method Summary collapse

Class Method Details

.alter_column(klass, old_field, new_field) ⇒ Object

NOT IMPLEMENTED



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# File 'lib/n/db/tools.rb', line 99

def self.alter_column(klass, old_field, new_field)
end

.alter_table(klass) ⇒ Object

Lets say you have changed the definition of a managed object (for example you have added a new prop_accessor, and want to automatically update the database schema. Compares the given class to the actual db schema and automatically alters the backend table if needed. No need to optimize this method.



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# File 'lib/n/db/tools.rb', line 29

def self.alter_table(klass)
	#
	# Use the following query to see the fields in system level:
	#
	# sql  = "SELECT attname, attnum FROM pg_attribute, pg_class "
	# sql << "WHERE attrelid = pg_class.oid " 
	# sql << "AND relname = '#{klass::DBTABLE}' AND attnum > 0;"
	#
	# In orer to test alter_table() use the following tests:
	#
	# klass.__props << N::Property.new("new_field", String)
	# klass.__props.delete_if{ |member| member.name == "new_field" }
	#
	# Remember you must not uncomment both of the above statements.
	# Uncomment the first one, use alter_table(), the uncomment the
	# seconde one and re-use alter_table().
	#
	$db.open { |db|
		
		sql = "SELECT * FROM #{klass::DBTABLE} LIMIT 1;"			
		table_fields = db.exec(sql).fields

		# find fields to be added.
		properties_to_add = []
		klass.__props.each { |klass_member|
			properties_to_add << klass_member unless table_fields.include? klass_member.name	
		}

		# find fields to be removed.
		properties_to_remove = []
		table_fields.each { |field|
			properties_to_remove << field unless klass.__props.map{ |member| member.name }.include? field
		}

		# Add new fields
		fields = []
		properties_to_add.each { |p|
			field = "#{p.symbol}"
			if p.sql
				field << " #{p.sql}"
			else
				field << " #{db.class::TYPEMAP[p.klass]}"
			end
			field << " #{p.sql}" if p.sql
		
			fields << field 
		}
	
		for field in fields
			sql = "ALTER TABLE #{klass::DBTABLE} ADD COLUMN #{field}"
			db.exec_clear(sql)
		end
		
		removed = nil
		properties_to_remove.each { |p|
			sql = "ALTER TABLE #{klass::DBTABLE} DROP COLUMN #{p} RESTRICT"
			db.exec_clear(sql)
			removed = true
		}

		if removed
			sql = "UPDATE #{klass::DBTABLE}; VACUUM FULL #{klass::DBTABLE};"
			db.exec_clear(sql)
		end
		
	}
end

.rename_table(old_klass, new_klass) ⇒ Object

NOT IMPLEMENTED



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# File 'lib/n/db/tools.rb', line 104

def self.rename_table(old_klass, new_klass)
end