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C# (/ ˌ s iː ˈ ʃ ɑːr p / see SHARP) [b] is a general-purpose high-level programming language supporting multiple paradigms.C# encompasses static typing, [16]: 4 strong typing, lexically scoped, imperative, declarative, functional, generic, [16]: 22 object-oriented (class-based), and component-oriented programming disciplines.
For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can only contain either null values or values from a parent table's primary key or a candidate key. [2] In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table. For ...
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
This is a feature of C# 9.0. Similar to in scripting languages, top-level statements removes the ceremony of having to declare the Program class with a Main method. Instead, statements can be written directly in one specific file, and that file will be the entry point of the program. Code in other files will still have to be defined in classes.
Surrogate keys simplify the creation of foreign key relationships because they only require a single column (as opposed to composite keys - which require multiple columns). When creating a query on the database, forgetting to include all the columns in a composite foreign key when joining tables can lead to unexpected results in the form of an ...
Foreign keys may be the primary key in another table; for example a PersonID may become the EmployeeID in the Employee table. In this case, the EmployeeID is both a foreign key and the unique primary key, meaning that the tables have a 1:1 relationship.
Comparison of C# and Visual Basic .NET; Comparison of Visual Basic and Visual Basic .NET; ... */" often found in C-based languages, but with two differences.
The following example uses Entity Framework and configures the TodoList class to be stored in the database table Lists and defines a primary and a foreign key. The code should be understood more or less as: "A TodoList has key TodoListID, its entity set name is Lists and it has many TodoItem's each of which has a required TodoList".