or_()#

relationalai.InstanceProperty
InstanceProperty.or_(other: Any) -> InstanceProperty

Produces a default property value for objects for which the value is None or that lack the property all together. Returns an InstanceProperty that produces the original values, along with the default value other. Must be used in a rule or query context.

Parameters#

NameTypeDescription
otherAnyThe default property value. Supported types include Producer objects, numbers, strings, dates, and datetime objects. For optimal performance, the type should match the values produced by the InstanceProperty.

Returns#

An InstanceProperty object.

Example#

Use .or_() to assign a default property value to objects where the property is either unset or set to None:

import relationalai as rai

# Create a model named "books" with a Book type.
model = rai.Model("books")
Book = model.Type("Book")

# Add some books to the model.
with model.rule():
    Book.add(title="Foundation", author="Isaac Asimov")
    Book.add(title="Dune", author="Frank Herbert")
    Book.add(title="Sir Gowain and the Green Knight")

# Get the title and publication year of all books.
with model.query() as select:
    # Get all book objects.
    book = Book()
    # Select the title and author properties of the books.
    # `.or_()` sets a default value of "Unknown" for books without an author.
    response = select(book.title, book.author.or_("Unknown"))

print(response.results)
# Output:
#                              title         author
# 0                             Dune  Frank Herbert
# 1                       Foundation   Isaac Asimov
# 2  Sir Gowain and the Green Knight        Unknown

Above, book is an Instance that produces Book objects. book.author.or_("Unknown") returns an InstanceProperty that produces the author’s name or "Unknown" if the book lacks an author property, such as in “Sir Gawain and the Green Knight.”

Without .or_(), the query outputs None for books lacking an author. In the resulting pandas DataFrame, None may appear as NaN, depending on the column type:

# Get the title and publication year of all books.
with model.query() as select:
    book = Book()
    response = select(book.title, book.author)  # .or() is not used.

print(response.results)
# Output:
#                              title         author
# 0                             Dune  Frank Herbert
# 1                       Foundation   Isaac Asimov
# 2  Sir Gowain and the Green Knight            NaN

.or_() also works with multi-valued properties created using .add() or .extend():

# Add genres to the books.
# genres is a multi-valued property because it is created with Instance.extend().
with model.rule():
    Book(title="Foundation").genres.extend(["Science Fiction"])
    Book(title="Dune").genres.extend(["Science Fiction", "Adventure"])

# Get the genres of all books.
with model.query() as select:
    book = Book()
    # Select the title and genres properties of the books.
    # `.or_()` sets a default value of "Unknown" for books without genres.
    response = select(book.title, book.genres.or_("Unknown"))

print(response.results)
# Output:
#                              title           genres
# 0                             Dune        Adventure
# 1                             Dune  Science Fiction
# 2                       Foundation  Science Fiction
# 3  Sir Gowain and the Green Knight          Unknown

See Also#