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Database Objects (Wt::Dbo)

An implemenation of an Object Relational Mapping layer. More...

Classes

class  Wt::Dbo::ForeignKeyConstraint
 Type that indicates one or more foreign key constraints. More...
 
struct  Wt::Dbo::ptr_tuple< T0, T1,, T9 >
 A utility class for defining a tuple of database objects. More...
 
class  Wt::Dbo::SqlStatement
 Abstract base class for a prepared SQL statement. More...
 
class  Wt::Dbo::backend::Firebird
 A Firebird connection. More...
 
class  Wt::Dbo::backend::MySQL
 A MySQL connection. More...
 
class  Wt::Dbo::backend::Postgres
 A PostgreSQL connection. More...
 
class  Wt::Dbo::backend::Sqlite3
 An SQLite3 connection. More...
 
class  Wt::Dbo::collection< C >
 An STL container for iterating query results. More...
 
class  Wt::Dbo::Exception
 Exception base class for Wt::Dbo. More...
 
class  Wt::Dbo::StaleObjectException
 Exception thrown when Wt::Dbo detects a concurrent modification More...
 
class  Wt::Dbo::ObjectNotFoundException
 Exception thrown when trying to load a non-existing object. More...
 
class  Wt::Dbo::NoUniqueResultException
 Exception thrown when a query unexpectedly finds a non-unique result. More...
 
class  Wt::Dbo::FixedSqlConnectionPool
 A connection pool of fixed size. More...
 
class  Wt::Dbo::JsonSerializer
 An action to serialize objects to JSON. More...
 
class  Wt::Dbo::dbo_default_traits
 Default traits for a class mapped with Wt::Dbo. More...
 
class  Wt::Dbo::dbo_traits< C >
 Traits for a class mapped with Wt::Dbo. More...
 
class  Wt::Dbo::Dbo< C >
 A base class for database objects. More...
 
class  Wt::Dbo::ptr< C >
 A smart pointer for a database object. More...
 
class  Wt::Dbo::Query< Result, BindStrategy >
 A database query. More...
 
class  Wt::Dbo::QueryModel< Result >
 A Wt MVC Model to view/edit query results. More...
 
class  Wt::Dbo::Session
 A database session. More...
 
class  Wt::Dbo::SqlConnection
 Abstract base class for an SQL connection. More...
 
class  Wt::Dbo::SqlConnectionPool
 Abstract base class for a SQL connection pool. More...
 
class  Wt::Dbo::sql_value_traits< V, Enable >
 Traits class for value types. More...
 
class  Wt::Dbo::FieldInfo
 Description of a field. More...
 
class  Wt::Dbo::query_result_traits< Result >
 Traits class for result types. More...
 
class  Wt::Dbo::Transaction
 A database transaction. More...
 
class  Wt::Dbo::weak_ptr< C >
 A weak pointer for a database object. More...
 

Enumerations

enum  Wt::Dbo::RelationType { Wt::Dbo::ManyToOne, Wt::Dbo::ManyToMany }
 Type of an SQL relation. More...
 

Functions

ForeignKeyConstraint Wt::Dbo::operator| (ForeignKeyConstraint lhs, ForeignKeyConstraint rhs)
 Combines two constraints.
 
template<class Action , typename V >
void Wt::Dbo::id (Action &action, V &value, const std::string &name="id", int size=-1)
 Maps a natural primary key (id) field. More...
 
template<class Action , class C >
void Wt::Dbo::id (Action &action, ptr< C > &value, const std::string &name, ForeignKeyConstraint constraints, int size=-1)
 Maps a natural primary key (id) field that is a foreign key. More...
 
template<class Action , typename V >
void Wt::Dbo::field (Action &action, V &value, const std::string &name, int size=-1)
 Maps a database object field. More...
 
template<class Action , class C >
void Wt::Dbo::belongsTo (Action &action, ptr< C > &value, const std::string &name=std::string(), int size=-1)
 Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation. More...
 
template<class Action , class C >
void Wt::Dbo::belongsTo (Action &action, ptr< C > &value, const std::string &name, ForeignKeyConstraint constraints, int size=-1)
 Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation. More...
 
template<class Action , class C >
void Wt::Dbo::belongsTo (Action &action, ptr< C > &value, ForeignKeyConstraint constraints, int size=-1)
 Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation. More...
 
template<class Action , class C >
void Wt::Dbo::hasOne (Action &action, weak_ptr< C > &value, const std::string &name=std::string())
 Maps the "One"-side of a OneToOne relation. More...
 
template<class Action , class C >
void Wt::Dbo::hasMany (Action &action, collection< ptr< C > > &value, RelationType type, const std::string &name=std::string())
 Maps the "Many"-side of a ManyToOne or ManyToMany relation. More...
 
template<class Action , class C >
void Wt::Dbo::hasMany (Action &action, collection< ptr< C > > &value, RelationType type, const std::string &name, const std::string &joinId, ForeignKeyConstraint constraints=(NotNull|OnDeleteCascade))
 Maps the "Many"-side of a ManyToMany relation. More...
 

Variables

const ForeignKeyConstraint Wt::Dbo::NotNull
 A constraint that prevents a null ptr. More...
 
const ForeignKeyConstraint Wt::Dbo::OnUpdateCascade
 A constraint that cascades updates. More...
 
const ForeignKeyConstraint Wt::Dbo::OnUpdateSetNull
 A constraint that cascades updates. More...
 
const ForeignKeyConstraint Wt::Dbo::OnDeleteCascade
 A constraint that cascades deletes. More...
 
const ForeignKeyConstraint Wt::Dbo::OnDeleteSetNull
 A constraint that cascades deletes. More...
 

Detailed Description

An implemenation of an Object Relational Mapping layer.

For an introduction, see the tutorial.

Enumeration Type Documentation

Type of an SQL relation.

Enumerator
ManyToOne 

Many-to-One relationship.

ManyToMany 

Many-to-Many relationship.

Function Documentation

template<class Action , class C >
void Wt::Dbo::belongsTo ( Action &  action,
ptr< C > &  value,
const std::string &  name = std::string(),
int  size = -1 
)

Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation.

This function binds the pointer field value to the database foreign key field(s) name + "_" + (C's primary key(s)).

If the name is omitted or empty, then C's mapped table name is used.

A belongsTo() will usually have a counter-part hasMany() or hasOne() declaration in the referenced class C.

See Also
hasMany()
template<class Action , class C >
void Wt::Dbo::belongsTo ( Action &  action,
ptr< C > &  value,
const std::string &  name,
ForeignKeyConstraint  constraints,
int  size = -1 
)

Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation.

This overloaded method allows to specify constraints for the foreign key.

See Also
hasMany()
template<class Action , class C >
void Wt::Dbo::belongsTo ( Action &  action,
ptr< C > &  value,
ForeignKeyConstraint  constraints,
int  size = -1 
)

Maps the "One"-side (foreign key) of a ManyToOne or OneToOne relation.

This overloaded method allows to specify constraints for the foreign key.

See Also
hasMany()
template<class Action , typename V >
void Wt::Dbo::field ( Action &  action,
V &  value,
const std::string &  name,
int  size = -1 
)

Maps a database object field.

This function binds the field value to the database field name.

The optional size may be used as a hint for the needed storage. It is only useful for std::string or Wt::WString fields, and causes the schema to use a varchar(size) for storing the field instead of an unlimited length string type.

You may want to specialize this method for a particular composite type which should be persisted in multiple database fields but not as a separate table (e.g. for natural composite primary keys, see id()).

For example:

struct Coordinate {
int x, y;
};
namespace Wt {
namespace Dbo {
template <class Action>
void field(Action& action, Coordinate& coordinate, const std::string& name, int size = -1)
{
field(action, coordinate.x, name + "_x");
field(action, coordinate.y, name + "_y");
}
} // namespace Dbo
} // namespace Wt

To support a custom type that needs to be persisted as a single field, you should specialize sql_value_traits instead.

template<class Action , class C >
void Wt::Dbo::hasMany ( Action &  action,
collection< ptr< C > > &  value,
RelationType  type,
const std::string &  name = std::string() 
)

Maps the "Many"-side of a ManyToOne or ManyToMany relation.

This function binds the collection field value to contain objects (of type C) that holds the associated objects: reading from the collection and adding or removing objects from the collection results in SQL statements.

For a ManyToOne relation, the query is defined by the database field(s) name + "_" + (C's primary key(s)), in the mapped table for C. This should be the same name as passed to the matching belongsTo() method for the other side of the relation. If the name is omitted or empty, then the mapped table name of the current class is used.

For a ManyToMany relation, the name is the name of a linker table (this linker table may be schema qualified, e.g. "myschema.posts_tags". Thus, also for a ManyToMany relation, both sides of the relationship will have the same name passed to them. In the join table, this side of the the relation will be referenced using the table name + "_" + (primary key(s)) of the current class.

A hasMany() must have a counter-part belongsTo() or hasMany() declaration in the referenced class C.

See Also
belongsTo()
template<class Action , class C >
void Wt::Dbo::hasMany ( Action &  action,
collection< ptr< C > > &  value,
RelationType  type,
const std::string &  name,
const std::string &  joinId,
ForeignKeyConstraint  constraints = (NotNull|OnDeleteCascade) 
)

Maps the "Many"-side of a ManyToMany relation.

This function binds the collection field value to contain objects (of type C).

This overloaded method allows to customize the field name of the foreign id in the join table, and specify constraints for this foreign key. The only allowed value for type is ManyToMany.

The joinId is used to reference this side of the relationship in the join table. If joinId is left blank, the value will be table name + "_" + (primary key(s)) of the current class.

A hasMany() must have a counter-part belongsTo() or hasMany() declaration in the referenced class C.

See Also
belongsTo()
template<class Action , class C >
void Wt::Dbo::hasOne ( Action &  action,
weak_ptr< C > &  value,
const std::string &  name = std::string() 
)

Maps the "One"-side of a OneToOne relation.

This function binds the weak_ptr field value to the associated object (of type C).

A weak_ptr is required here to break the cycle that would otherwise be created by the hasOne() and belongsTo() associations. The value is not actually stored but defined in terms of a SQL query (not that different from how a hasMany() call backs a collection by a SQL query).

The query is defined by the database field(s) name + "_" + (C's primary key(s)), in the mapped table for C. This should be the same name as passed to the matching belongsTo() method for the other side of the relation. If the name is omitted or empty, then the mapped table name of the current class is used.

A hasOne() must have a counter-part belongsTo() declaration in the referenced class C.

See Also
belongsTo()
template<class Action , typename V >
void Wt::Dbo::id ( Action &  action,
V &  value,
const std::string &  name = "id",
int  size = -1 
)

Maps a natural primary key (id) field.

A natural primary key field is optional. If you define one and its type is not long long, you must specialize Wt::Dbo::dbo_traits to match the type V as the IdType for this class. When not specified for a class, an auto-generated surrogate key field is used with the name specified by Wt::Dbo::dbo_traits::surrogateIdField(), which defaults to "id".

Unlike the default surrogate key, a natural id is not auto-generated and thus you need to give each object a unique value when creating a new object.

The id may be a composite type. In that case, you need to specialize Wt::Dbo::field().

template<class Action , class C >
void Wt::Dbo::id ( Action &  action,
ptr< C > &  value,
const std::string &  name,
ForeignKeyConstraint  constraints,
int  size = -1 
)

Maps a natural primary key (id) field that is a foreign key.

This overloaded method allows to specify constraints for the foreign key.

See Also
hasMany()

Variable Documentation

const ForeignKeyConstraint Wt::Dbo::NotNull

A constraint that prevents a null ptr.

A database constraint which prevents that a ptr references no object and has a value of null.

const ForeignKeyConstraint Wt::Dbo::OnDeleteCascade

A constraint that cascades deletes.

A database constraint which propagates deletes of the referenced object to also delete the object(s) that reference it.

Note
This constraint only affects the database schema creation.
const ForeignKeyConstraint Wt::Dbo::OnDeleteSetNull

A constraint that cascades deletes.

A database constraint which propagates deletes of the referenced object to also delete the objects that reference.

Note
This constraint only affects the database schema creation.
const ForeignKeyConstraint Wt::Dbo::OnUpdateCascade

A constraint that cascades updates.

A database constraint which propagates updates to the natural primary key in the referenced table.

Note
This constraint only affects the database schema creation. Currently it is not possible to update a natural Id of an already saved object through Dbo itself.
const ForeignKeyConstraint Wt::Dbo::OnUpdateSetNull

A constraint that cascades updates.

A database constraint which sets the value of the ptr to null when the referenced primary key changes.

Note
This constraint only affects the database schema creation. Currently it is not possible to update a natural Id of an already saved object through Dbo itself.

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