from google.appengine.ext import ndb

# Datastore Model for a Student.
class Student(ndb.Model):
    first_name = ndb.StringProperty()
    last_name = ndb.StringProperty()
    credits = ndb.IntegerProperty()

########################################
# Modeling Relationships in Datastore #
########################################

# Datastore Model for a Wand that stores a reference to its owner.
class Wand(ndb.Model):
    core = ndb.StringProperty()
    wood_type = ndb.StringProperty()
    model = ndb.IntegerProperty()
    length = ndb.FloatProperty()
    # 'owner' is a reference to a Student via a Key.
    owner = ndb.KeyProperty(kind="Student")

##### Set up the data. Add a student and their wand.
# Make a Student to represent Ginny Weasley.
ginny = Student(first_name="Ginny", last_name="Weasley", credits=0)
# Add to the datastore and store the Key that was returned.
ginny_key = ginny.put()

# Create a Wand for Ginny, using her Key as the 'owner' value.
new_wand = Wand(core="voldemort", length=6.66, owner=ginny_key)
# Add the wand to the datastore.
new_wand_key = new_wand.put()

##### Find the wand owner's first name, by following its 'owner'.
# 1. Get the Key stored in the wand.
owner_key = new_wand.owner
# 2. Use Key's .get() method to retrieve the full entity.
owner_entity = owner_key.get()
# 3. Print their first name.
print owner_entity.first_name

###########
# Queries #
###########

# Uncomment to add some data to work with if your datastore is empty.
# harry = Student(first_name="Harry", last_name="Potter", credits=45)
# harry.put()
# hermione = Student(first_name="Hermione", last_name="Granger", credits=100000)
# hermione.put()

### Retrieve all entities of a certain class/kind with .query() and .fetch().
# 1. Set up the query (the question).
student_query = Student.query()
# 2. Execute the query by calling .fetch() and store the list of results.
all_students = student_query.fetch()
# 3. Iterate over results and print them one per line.
print
print "All Students:"
for student in all_students:
    print student

### Retrieve the first single matching entity by calling .get() instead of
### .fetch().
first_student = student_query.get()
print
print "First student:"
print student

### Filter results with .query(filter_expression)
# Find the entities with more than 60 credits.
student_filter_query = Student.query(Student.credits > 60)
all_students = student_filter_query.fetch()
print
print "Students with more than 60 credits:"
for student in all_students:
    print student

### Sort results with .order(sort_criteria).
# Sort students by last name (alphabetically).
student_ordered_query = student_query.order(Student.last_name)
ordered_students = student_ordered_query.fetch()
print
print "Students listed alphabetically by last name:"
for student in ordered_students:
    print student
# You can reverse the sort by prefixing with a '-'.
student_reverse_ordered_query = student_query.order(-Student.last_name)
reverse_ordered_students = student_reverse_ordered_query.fetch()
print
print "Students listed alphabetically in reverse by last name:"
for student in reverse_ordered_students:
    print student

### Limit results with .fetch(limit)
# Get the first 5 students.
five_students = student_query.fetch(limit=5)
print
print "First 5 students:"
for student in five_students:
    print student