Class: Og::Backend

Inherits:
Object show all
Defined in:
lib/og/backend.rb

Overview

Abstract backend. A backend communicates with the RDBMS. This is the base class for the various backend implementations.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config) ⇒ Backend

Intitialize the connection to the RDBMS.



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# File 'lib/og/backend.rb', line 21

def initialize(config)
	raise "Not implemented"
end

Instance Attribute Details

#conn ⇒ Object

The actual connection to the database



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# File 'lib/og/backend.rb', line 17

def conn
  @conn
end

Class Method Details

.create_db(database, user = nil, password = nil) ⇒ Object

Create the database.



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# File 'lib/og/backend.rb', line 173

def self.create_db(database, user = nil, password = nil)
	Logger.info "Creating database '#{database}'."
end

.drop_db(database, user = nil, password = nil) ⇒ Object

Drop the database.



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# File 'lib/og/backend.rb', line 179

def self.drop_db(database, user = nil, password = nil)
	Logger.info "Dropping database '#{database}'."
end

.encode(klass) ⇒ Object

Encode the name of the klass as an sql safe string. The Module separators are replaced with _ and NOT stripped out so that we can convert back to the original notation if needed. The leading module if available is removed.



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# File 'lib/og/backend.rb', line 40

def self.encode(klass)
	"#{klass.name.gsub(/^.*::/, "")}".gsub(/::/, "_").downcase
end

.eval_og_deserialize(klass, og) ⇒ Object

Precompile the code to read objects of the given class from the backend. In order to allow for changing field/attribute orders we have to use a field mapping hash.



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# File 'lib/og/backend.rb', line 146

def self.eval_og_deserialize(klass, og)
	calc_field_index(klass, og)
	
	props = klass.__props 
	code = []
	
	props.each do |p|
		if idx = og.managed_classes[klass].field_index[p.name]
			# more fault tolerant if a new field is added and it 
			# doesnt exist in the database.
			code << "@#{p.name} = #{read_prop(p, idx)}"
		end
	end
	
	klass.class_eval %{
 		def og_deserialize(res, tuple = nil)
			#{code.join('; ')}
		end
	}
end

.eval_og_insert(klass) ⇒ Object

Precompile the insert code for the given class. The generated code sets the oid when inserting!



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# File 'lib/og/backend.rb', line 67

def self.eval_og_insert(klass)
	props = props_for_insert(klass)
	
	values = props.collect { |p| write_prop(p) } 
	
	sql = "INSERT INTO #{table(klass)} (#{props.collect {|p| p.name}.join(',')}) VALUES (#{values.join(',')})"

	if klass.instance_methods.include?("og_pre_insert")
		pre_cb = "og_pre_insert(conn);"
	else
		pre_cb = ""
	end

	if klass.instance_methods.include?("og_post_insert")
		post_cb = "og_post_insert(conn);"
	else
		post_cb = ""
	end

	if klass.instance_methods.include?("og_pre_insert_update")
		pre_cb << "og_pre_insert_update(conn);"
	end

	if klass.instance_methods.include?("og_post_insert_update")
		post_cb << "og_post_insert_update(conn);"
	end
	
	klass.class_eval %{
		def og_insert(conn)
			#{insert_code(klass, sql, pre_cb, post_cb)}
		end
	}
end

.eval_og_update(klass) ⇒ Object

Precompile the update code for the given class. Ignore the oid when updating!



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# File 'lib/og/backend.rb', line 104

def self.eval_og_update(klass)
	props = klass.__props.reject { |p| :oid == p.symbol }
	
	updates = props.collect { |p|
		"#{p.name}=#{write_prop(p)}"
	}

	sql = "UPDATE #{klass::DBTABLE} SET #{updates.join(', ')} WHERE oid=#\{@oid\}"

	if klass.instance_methods.include?("og_pre_update")
		pre_cb = "og_pre_update(conn);"
	else
		pre_cb = ""
	end

	if klass.instance_methods.include?("og_post_update")
		post_cb = "og_post_update(conn);"
	else
		post_cb = ""
	end

	if klass.instance_methods.include?("og_pre_insert_update")
		pre_cb << "og_pre_insert_update(conn);"
	end

	if klass.instance_methods.include?("og_post_insert_update")
		post_cb << "og_post_insert_update(conn);"
	end
	
	klass.class_eval %{
		def og_update(conn)
			#{pre_cb}
			conn.exec "#{sql}"
			#{post_cb}
		end
	}
end

.join_table(klass1, klass2) ⇒ Object

The name of the join table for the two given classes.



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# File 'lib/og/backend.rb', line 53

def self.join_table(klass1, klass2)
	"_#{Og.table_prefix}j_#{encode(klass1)}_#{encode(klass2)}"
end

.props_for_insert(klass) ⇒ Object

Returns the props that will be included in the insert query. For some backends the oid should be stripped.



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# File 'lib/og/backend.rb', line 60

def self.props_for_insert(klass)
	klass.__props
end

.table(klass) ⇒ Object

The name of the SQL table where objects of this class are stored.



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# File 'lib/og/backend.rb', line 47

def self.table(klass)
	"_#{Og.table_prefix}#{encode(klass)}"
end

Instance Method Details

#close ⇒ Object

Close the connection to the RDBMS.



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# File 'lib/og/backend.rb', line 27

def close()
	@conn.close()
end

#commit ⇒ Object

Commit a transaction.



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# File 'lib/og/backend.rb', line 223

def commit
	exec "COMMIT"
end

#create_fields(klass, typemap) ⇒ Object

Create the fields that correpsond to the klass properties. The generated fields array is used in create_table. If the property has an :sql metadata this overrides the default mapping. If the property has an :extra_sql metadata the extra sql is appended after the default mapping.



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# File 'lib/og/backend.rb', line 239

def create_fields(klass, typemap)
	fields = []
	
	klass.__props.each do |p|
		klass.sql_index(p.symbol) if p.meta[:sql_index]
			
		field = "#{p.symbol}"
		
		if p.meta and p.meta[:sql]
			field << " #{p.meta[:sql]}"
		else
			field << " #{typemap[p.klass]}"
			# attach extra sql
			if p.meta and extra_sql = p.meta[:extra_sql]
				field << " #{extra_sql}"
			end
		end
		
		fields << field 
	end

	return fields
end

#create_table(klass) ⇒ Object

Create the managed object table. The properties of the object are mapped to the table columns. Additional sql relations and constrains are created (indicices, sequences, etc).



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# File 'lib/og/backend.rb', line 267

def create_table(klass)
	return if query("SELECT * FROM #{klass::DBTABLE} LIMIT 1")
end

#deserialize_all(res, klass) ⇒ Object

Deserialize all rows of the resultset.



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# File 'lib/og/backend.rb', line 285

def deserialize_all(res, klass)	
	raise 'Not implemented'
end

#deserialize_one(res, klass) ⇒ Object

Deserialize one row of the resultset.



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# File 'lib/og/backend.rb', line 279

def deserialize_one(res, klass)	
	raise 'Not implemented'
end

#drop_table(klass) ⇒ Object

Drop the managed object table



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# File 'lib/og/backend.rb', line 273

def drop_table(klass)
	exec "DROP TABLE #{klass::DBTABLE}"
end

#exec(sql) ⇒ Object

Execute an SQL query, no result returned.



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# File 'lib/og/backend.rb', line 191

def exec(sql)
	raise "Not implemented"
end

#get_int(res, idx = 0) ⇒ Object

Return a single integer value from the resultset.



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# File 'lib/og/backend.rb', line 291

def get_int(res, idx = 0)
	raise 'Not implemented'
end

#query(sql) ⇒ Object

Execute an SQL query and return the result.



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# File 'lib/og/backend.rb', line 185

def query(sql)
	raise "Not implemented"
end

#rollback ⇒ Object

Rollback transaction.



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# File 'lib/og/backend.rb', line 229

def rollback
	exec "ROLLBACK"
end

#safe_exec(sql) ⇒ Object

Execute an SQL query, no result returned. Wrapped in a rescue block.



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# File 'lib/og/backend.rb', line 205

def safe_exec(sql)
	raise "Not implemented"
end

#safe_query(sql) ⇒ Object

Execute an SQL query and return the result. Wrapped in a rescue block.



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# File 'lib/og/backend.rb', line 198

def safe_query(sql)
	raise "Not implemented"
end

#start ⇒ Object

Start a new transaction.



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# File 'lib/og/backend.rb', line 217

def start
	exec "START TRANSACTION"
end

#valid?(res) ⇒ Boolean

Check if it is a valid resultset.

Returns:

  • (Boolean) 


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# File 'lib/og/backend.rb', line 211

def valid?(res)
	raise "Not implemented"
end