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SQLAlchemy offers tools for database schema generation, querying, and object-relational mapping. Key features include: A comprehensive embedded domain-specific language for SQL in Python called "SQLAlchemy Core" that provides means to construct and execute SQL queries. A powerful ORM that allows the mapping of Python classes to database tables.
Many data description languages use a declarative syntax to define columns and data types. Structured Query Language (SQL), however, uses a collection of imperative verbs whose effect is to modify the schema of the database by adding, changing, or deleting definitions of tables or other elements.
The function to extract the key value from the object is specified by the user as a delegate. Reverse The Reverse operator reverses a collection. GroupBy The GroupBy operator takes a function that extracts a key value and returns a collection of IGrouping<Key, Values> objects, for each distinct key value.
Dynamic set structures typically add: create(): creates a new, initially empty set structure. create_with_capacity(n): creates a new set structure, initially empty but capable of holding up to n elements. add(S,x): adds the element x to S, if it is not present already. remove(S, x): removes the element x from S, if it is present.
Set-Membership constraints: The values for a column come from a set of discrete values or codes. For example, a person's sex may be Female, Male or Non-Binary. Foreign-key constraints: This is the more general case of set membership. The set of values in a column is defined in a column of another table that contains unique values.
Adding negation to Datalog complicates its semantics, leading to whole new languages and strategies for evaluation. For example, the language that results from adding negation with the stable model semantics is exactly answer set programming. Stratified negation can be added to Datalog while retaining its model-theoretic and fixed-point ...
In computer science, an associative array, map, symbol table, or dictionary is an abstract data type that stores a collection of (key, value) pairs, such that each possible key appears at most once in the collection. In mathematical terms, an associative array is a function with finite domain. [1] It supports 'lookup', 'remove', and 'insert ...
A fluent interface is normally implemented by using method chaining to implement method cascading (in languages that do not natively support cascading), concretely by having each method return the object to which it is attached [citation needed], often referred to as this or self.