Eldorado.Object.Query

Queries can be composed and checked against the domain model. Precisely how a query is to be executed is out of the scope of this aspect (though the semantics of the operators ARE in this scope).

Examples of queries include:

select p from Project p
This query denotes the set of all projets. The result set contains one column named "p" which represents the oid of the project.
This query can serve several purposes:

To collect the Project entities present in the local storage (method ObjectContext.LocalStorage.Collect).
To collect the Project entities present in the local storage after a lazy loading from the database (method ObjectContext.Collect).
To fill a DataSet with a one column DataTable (method RemoteSource.Fill).
To get a DataReader (method RemoteSource.GetDataReader).
To count the number of Project entities (method RemoteSource.GetCount).

select p, p.Name, p.Budget from Project p
This query denotes the set of all projets. The result set contains three columns named "p", "Name" and "Budget" which represent the oid of the project, its name and its budget.
Contrary to the preceeding query, this query cannot be used with the Collect methods: the columns denoted by this query do not exactly match a particular entity (some columns may be missing to match the "Project" entity). On the other hand, the Fill, GetDataReader and GetCount can perfectly accept such a query.

select p from Project p order by p.Budget desc
This query denotes the set of all projets by decreasing order of budget.

select p, p.Name, p.Budget, m.Name as Manager from Project p, p.Manager m
This query denotes the set of all projets with their manager's name. This query specifies a join "p.Manager m" where "Manager" is a reference declared on type "Project". This is an inner join: only those project that have a manager will be returned.
The result set contains four columns named "p", "Name", "Budget" and "Manager".

select p, p.Name, p.Budget, m.Name as Manager from Project p, p.Manager m where m.Name like ?
This query denotes the set of all projets with whose manager's name matches a particular parameter.

select p, p.Name, p.Budget, m.Name as Manager from Project p, p.Manager? m
This query denotes the set of all projets with their manager's name. This query specifies an outer join "p.Manager m?" (note the "?" sign): all projects will be returned. Those that do not have a manager will have their column "Manager" set to null.

select p, p.Name, p.Budget, m.Name as Manager from Project p, p.Manager? m where m.Name like ? order by p.Budget desc
This query shows a combination of the different operators seen above.

Namespace hierarchy

Classes

Class	Description
Correlation	A variable defined in the from clause of an ObjectPath
CrossPath	Cartesian product in an ObjectPath.
FilterPath	Where clause in an ObjectPath.
IntersectPath	"Where in" or "where not in" clause in an ObjectPath.
JoinPath	Join clause in an ObjectPath.
ObjectPath	The from and where clauses of an ObjectQuery
ObjectQuery	A select query over an ObjectDomain.
ParseException	The type of exception thrown by the query parser.
ScanPath	The from clause of an ObjectQuery.

Interfaces

Interface	Description
IObjectPathEvaluator	Object that knows how to evaluate an ObjectPath.

Eldorado.Object.Query Namespace

Classes

Interfaces