Rails Many-to-many relationships and polymorphism

1. Many-to-many relationships and the realization of multi-state students, courses, teachers

The relationship between the three is many-to-many, who shows the polymorphism of the class

Model Layer

Stu.rb

Has_many:summaries

Has_many:subjects,: Through =>:summaries,: Source =: Subject #实现多对多关系

Teacher.rb

Has_many:summaries,:as =:p eople,:d ependent =:d Estroy #实现多态

Has_many:subjects,: Through =>:summaries,: Source =: Subject #实现多对多关系

Subject.rb

Has_many:summaries

Has_many:teachers,: Through =>:summaries,: Source =:p Eople,: source_type = ' Teacher '

Has_many:stus,: through = Summaries,:source =:p eople,: source_type = ' Stu '

Summary.rb

Class Summary <activerecord::base

Belongs_to:p eople,:p olymorphic = True

Belongs_to:subject

End

Db/migrate Layer

Summary.rb

Create_table:summaries do |t|

t.integer:subject_id

T.string:p Eople_type

T.integer:p eople_id

End

Cases:

s = subject.new

t = teacher.new

S.teachers <<t

S.save

The data in the summary table is now updated

2, Name_scope (need to use the class name to call)

A) Named_scope:sub_stu,: conditions = "Shangke_type is null"

b) Named_scope:sub_stu,: conditions = "Shangke_type is null" do

def get_count

All.count:conditions = "id = 1"

End

End

This approach is equivalent to the way the DEF definition is performed on the contents of the conditions condition lookup. But in real execution, the DEF-defined method is converted into an SQL statement, executed with the condition statement.