sqt::AssignmentType Concept Reference

#include <sqt/orm/expression/assignment_type.h>

Description

Constrains a type to be an assignment type, which associates an identifier with a value.

Requirements

• The type must satisfy the sqt::ExpressionLike concept.
• The type must have a static constant Operator of type sqt::AssignmentOperator.

Assignments are used in inserters and updaters to assign values to identifiers like columns, primary keys and indexes.

To create an assignment, use the assignment operator = on the identifier to assign a value or a placeholder. Consider the following entity type and its table definition:

struct MyEntity {
    int id{};
    std::string name;
};
SQT_TABLE_BEGIN(MyEntity, MyEntity)
SQT_COLUMN_FIELD(id, id)
SQT_COLUMN_FIELD(name, name)
SQT_PRIMARY_KEY(id)
SQT_INDEX(id, name)
SQT_TABLE_END

Examples of creating an inserter with assignments:

// Inserter with assignments of columns, using inline values.
auto inserter = sqt::DataContext<MyEntity>::MakeInserter(
    sqt::Table<MyEntity>.id = 1, 
    sqt::Table<MyEntity>.name = "The Name"
);
 
// Inserter with assignments of primary key and column, using placeholders.
auto inserter = sqt::DataContext<MyEntity>::MakeInserter(
    sqt::Table<MyEntity>.PrimaryKey = sqt::_,
    sqt::Table<MyEntity>.name = sqt::_
);
 
//Inserter with assignment of an index, which uses a composite value.
auto inserter = sqt::DataContext<MyEntity>::MakeInserter(
    sqt::Table<MyEntity>::Index_id_name = std::make_tuple(1, "The Name")
);

The sqt::Assignment<> class template satisfies this concept.

See also

sqt::Assignment<>

sqt::AssignmentOperator

sqt::ExpressionLike