EF core learning notes: additional foreign key attributes / single navigation attributes

Although we have been doing customized development , But you can't always eat what you want . Many things you must master .

Additional foreign key attributes  

Why do you need foreign key attributes

1、EF Core Foreign key columns will be created in the data table .

2、 If you need to get the value of the foreign key column , You need to do association query , Low efficiency .（ Various join）

3、 Need a kind of unnecessary Join Get the value of the foreign key column directly .

Set foreign key properties

1、 Explicitly declare a foreign key attribute in the entity class .

2、 Relationship configuration through HasForeignKey(c=>c.ArticleId) Specify this attribute as a foreign key .

3、 Unless necessary , Otherwise, don't declare , Because repetition will be introduced .

Then remember to configure ！ Otherwise EFcore I don't know where this foreign key comes from .

Review the hasOne( )

  Single navigation attribute

  The trouble of two-way navigation properties ： Many tables will refer to the same table , such ,user There will be many tables In reverse Navigation properties .

It is not necessary to

  So we need a single navigation attribute .

Requestor and Approved by All point to user surface

  Configuration method

Do not set the reverse attribute , And then when configuring WithMany() Do not set parameters .

How can one-way attributes get data in reverse

// Just check again ：
ctx.Leaves.Where(l => l.Requester == u)

For the master-slave structure “ One to many ” Table relations , It is generally to declare bidirectional navigation properties .

And for the rest “ One to many ” Table relations ： If the table belongs to the basic table referenced by many tables , Then use the single navigation attribute , Otherwise, you can freely decide whether to use the two-way navigation attribute .

  Considering the possibility of having a single navigation attribute , We usually use HasOne().WithMany()