No auto_inc of gorm:"primary_key" if foreignkey

If you are trying to create a table to store metadata about the
relationship of two entities, e.g. Product and Store and the quantity of
product available at that store. You may wish to use a composite foreign
key relationship.

If you also wish to use gorm to generate the SQL to create the schema,
but default gorm will add the auto_increment keyword to tables which are
both primary and integer. This is a undesirable for composite foreign
key relationships and generates invalid sql statements.

If you have a struct field which is a primary key and is marked as a
foreign key, disable the auto increment behavior while generating the
schema.

README.md

@@ -1116,6 +1116,21 @@ type Product struct {
 }
 ```
 
+## Composite Foreign Primary Integer Keys
+
+```go
+type ProductStore struct {
+       ProductID    int64 `gorm:"primary_key;foreignkey"`
+       StoreID 		int64 `gorm:"primary_key;foreignkey"`
+	   Quantity		int
+}
+```
+
+When you declare a gorm primary key as foreign, there is likely no good use case for also auto incrementing the field.
+This disables the auto increment behavior when creating the table from gorm.
+
+
+
 ## Database Indexes & Foreign Key
 
 ```go

model_struct.go

@@ -350,6 +350,10 @@ func (scope *Scope) generateSqlTag(field *StructField) string {
 			autoIncrease = true
 		}
 
+		if field.IsPrimaryKey && field.IsForeignKey {
+			autoIncrease = false
+		}
+
 		sqlType = scope.Dialect().SqlTag(reflectValue, size, autoIncrease)
 	}