Question

Does anyone have tried to implement an app in GAE having both java and python?

I have an existing app and my front end is in java. Now I want to use the existing datastore to be interfaced by python. My problem is i don’t know how to define the relationships and model that would be equivalent to the one in java. I have tried the one-to-many relationship in python but when stored in the datastore, the fields are different than the one-to-many of java.

My data classes are as follows.
//one-to-many owned

Parent Class

public class Parent{

    @PrimaryKey
    @Persistent
    private String unitID;
    //some other fields...


    @Persistent
    @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="dateCreated desc"))
    private List <Child>  child;

    //methods & constructors were omitted


}

Child

public class Child{

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key uId;

    @Persistent
    private String name;

    /* etc... */

}

Answer 1

Through some testing, I finally figured out how to do this. First is define the models or in java, it is called classes.

class Parent(db.Model):
    someData = db.StringProperty(multiline=True) ....

class Child(db.Model):
    someData = db.StringProperty(multiline=True) ...

Now, to set the relationship of an instance of a child to its parent, just set the parent as the ancestor of the child.

parentModel = Parent(key_name='key_of_parent')
childModel1 = Child(parent=parentModel) #set the parentModel as parent of the childModel1
childModel2 = Child(parent=parentModel) #set the parentModel as parent of the childModel2

Now you have an owned one-to-many relationship.