rename
add test
fix bug,

extract method in delete component command
extract method to minimize untestable code
delete file
rename,refine method
Extrace Load file as FileParser
erModel test
test ermodel
refactor
ERModelTest Done
1. rename fuction name in component

2. fix function in connector
3. test connector
test connector done
new collection hash map
change hash_map to HashMap
Convert hash_map variable to HashMap
refactor undo redo to testable code
refactor insert foreign key
Fix Convert table
Fix Command class
command pattern fix