class Instance

Instance is a subclass of Producer that produces model objects in rule and query contexts. They are created by calling a Type or the Type.add() method.


In addition to the methods inherited from Producer, Instance supports:

.set(*args, **kwargs)Set a Type or a property on an object.Instance


Instance objects act as variables representing model objects in rules and queries. Here’s how to create and manipulate an Instance:

import relationalai as rai

# Create a model named "people" with a Person type.
model = rai.Model("people")
Person = model.Type("Person")

# Add a person to the model.
with model.rule():
    # Add a person named "Kermit" to the model.
    # Person.add() returns an Instance.
    kermit = Person.add(name="Kermit")
    # Set Kermit's favorite color to "green" using Instance.set().

    # Add a person named "Rolf" to the model.
    rolf = Person.add(name="Rowlf")
    # Set Rolf's favorite color to "brown" using Instance.set().

with model.query() as select:
    # Get all Person objects.
    # Person() returns an Instance.
    person = Person()
    # Filter objects by name. == "Kermit"
    # Select the name and favorite_color properties of the Person objects.
    # Properties are accessed as Instance attributes.
    response = select(person.favorite_color)

# Output:
#      name favorite_color
# 0  Kermit          green

In the above example’s rule:

  1. Person.add(name="Kermit") returns an Instance that produces a Person object with a name property set to the string "Kermit".
  2. kermit.set(favorite_color="green") sets Kermit’s favorite_color property to the string "green". Property values may also be numbers, dates, datetime objects, or None. favorite_color is single-valued, meaning setting it a second time overwrites the previous value. See the .set() method docs for more information on single- and multi-valued properties. Note that kermit.set() returns the kermit instance, although it is not used here.

In the query:

  1. Person() returns an Instance that produces Person objects.
  2. == "Kermit" filters the objects produced by Person(), letting only those with the name "Kermit" pass through. Alternatively, you may combine this line with the first as person = Person(name="Kermit").
  3. select(person.favorite_color) selects the favorite_color property of the remaining objects. and person.favorite_color return InstanceProperty objects, a type of producer that represents object properties. The == operator returns an Expression, yet another type of producer that filters objects based on whether or not the expression evaluates to True.

See Also#