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Constructing Types (Entity SQL)

  • Článek

Entity SQL provides three kinds of constructors: row constructors, named type constructors, and collection constructors.

Row Constructors

You use row constructors in Entity SQL to construct anonymous, structurally typed records from one or more values. The result type of a row constructor is a row type whose field types correspond to the types of the values used to construct the row. For example, the following expression constructs a value of type Record(a int, b string, c int):

ROW(1 AS a, "abc" AS b, a + 34 AS c)

If you do not provide an alias for an expression in a row constructor, the Entity Framework will try to generate one. For more information, see the "Aliasing Rules" section in Identifiers (Entity SQL).

The following rules apply to expression aliasing in a row constructor:

  • Expressions in a row constructor cannot refer to other aliases in the same constructor.

  • Two expressions in the same row constructor cannot have the same alias.

For more information about row constructors, see ROW (Entity SQL).

Collection Constructors

You use collection constructors in Entity SQL to create an instance of a multiset from a list of values. All the values in the constructor must be of mutually compatible type T, and the constructor produces a collection of type Multiset<T>. For example, the following expression creates a collection of integers:

Multiset(1, 2, 3)

{1, 2, 3}

Empty multiset constructors are not allowed because the type of the elements cannot be determined. The following is not valid:

multiset() {}

For more information, see MULTISET (Entity SQL).

Named Type Constructors (NamedType Initializers)

Entity SQL allows type constructors (initializers) to create instances of named complex types and entity types. For example, the following expression creates an instance of a Person type.

Person("abc", 12)

The following expression creates an instance of a complex type.

MyModel.ZipCode(‘98118’, ‘4567’)

The following expression creates an instance of a nested complex type.

MyModel.AddressInfo('My street address', 'Seattle', 'WA', MyModel.ZipCode('98118', '4567'))

The following expression creates an instance of an entity with a nested complex type.

MyModel.Person("Bill", MyModel.AddressInfo('My street address', 'Seattle', 'WA', MyModel.ZipCode('98118', '4567')))

The following example shows how to initialize a property of a complex type to null. MyModel.ZipCode(‘98118’, null)

The arguments to the constructor are assumed to be in the same order as the declaration of the attributes of the type.

For more information, see Named Type Constructor (Entity SQL).

See Also

Concepts

Entity SQL Reference
Entity SQL Overview
Type System (Entity SQL)