IQueryCondition objects are specialized IReadCondition objects that allow the application to specify a filter on the locally available data. More...

Inheritance diagram for DDS.IQueryCondition:

Collaboration diagram for DDS.IQueryCondition:

Public Member Functions
string	GetQueryExpression ()
	This operation returns the query expression associated with the IQueryCondition. More...

ReturnCode	GetQueryParameters (ref string[] queryParameters)
	This operation obtains the query parameters associated with the IQueryCondition More...

ReturnCode	SetQueryParameters (params string[] queryParameters)
	This operation changes the query parameters associated with the IQueryCondition. More...

Public Member Functions inherited from DDS.IReadCondition
IDataReader	GetDataReader ()
	This operation returns the IDataReader associated with the IReadCondition. More...

InstanceStateKind	GetInstanceStateMask ()
	This operation returns the set of InstanceStates that are taken into account to determine the TriggerValue of the IReadCondition. More...

SampleStateKind	GetSampleStateMask ()
	This operation returns the set of SampleStates that are taken into account to determine the TriggerValue of the IReadCondition. More...

ViewStateKind	GetViewStateMask ()
	This operation returns the set of ViewStates that are taken into account to determine the TriggerValue of the IReadCondition. More...

Public Member Functions inherited from DDS.ICondition
bool	GetTriggerValue ()
	Each ICondition has a TriggerValue that can be true or false and is set by the DDS depending on the evaluation of the ICondition. More...

Detailed Description

IQueryCondition objects are specialized IReadCondition objects that allow the application to specify a filter on the locally available data.

The IDataReader objects accept a set of IQueryCondition objects for the IDataReader and provide support (in conjunction with IWaitSet objects) for an alternative communication style between the Data Distribution Service and the application (i.e., state-based rather than event-based).

Query Function

IQueryCondition objects allow an application to specify the data samples it is interested in (by specifying the desired sample-states, view-states, instance-states and query expression); see the parameter definitions for IDataReader's Read/Take operations. This allows the Data Distribution Service to trigger the condition only when suitable information is available. IQueryCondition objects are to be used in conjunction with an IWaitSet. More than one IQueryCondition may be attached to the same IDataReader.

The query (queryExpression) is similar to an SQL WHERE clause and can be parameterized by arguments that are dynamically changeable with the IQueryCondition.SetQueryParameters operation.

See also: Waitset

/* Simplified example of the creation of an QueryCondition
 * Defaults are used and possible errors are ignored. */
/* Prepare Domain. */
DDS.DomainParticipantFactory factory = DDS.DomainParticipantFactory.Instance;
DDS.IDomainParticipant participant = factory.CreateParticipant(DDS.DomainId.Default);
/* Create waitset */
IWaitSet waitset = new WaitSet();
/* Add topic data type to the system. */
DDS.ITypeSupport typesupport = new Space.FooTypeSupport();
DDS.ReturnCode retcode = typesupport.RegisterType(participant, "Space.Foo");
DDS.ITopic topic = participant.CreateTopic("SpaceFooTopic", "Space.Foo");
/* Create typed datareader. */
DDS.ISubscriber subscriber = participant.CreateSubscriber();
Space.FooDataReader reader = (Space.FooDataReader)publisher.CreateDataReader(topic);
/* Create querycondition */
string[] params = new string[1];
params[0] = "1";
IQueryCondition condition = reader.CreateQueryCondition("field = %0", params);
/* Attach condition to waitset */
retcode = waitset.AttachCondition(condition);

Definition at line 562 of file DdsDcpsInterfaces.cs.

Member Function Documentation

◆ GetQueryExpression()

string DDS.IQueryCondition.GetQueryExpression ( )

This operation returns the query expression associated with the IQueryCondition.

That is, the expression specified when the IQueryCondition was created. The operation will return null when there was an internal error or when the IQueryCondition was already deleted.

Returns: The query expression associated with the IQueryCondition.

◆ GetQueryParameters()

ReturnCode DDS.IQueryCondition.GetQueryParameters ( ref string [] queryParameters )

This operation obtains the query parameters associated with the IQueryCondition

That is, the parameters specified on the last successful call to IQueryCondition.SetQueryArguments or, if SetQueryArguments was never called, the arguments specified when the IQueryCondition were created.

The queryParameters parameter will contain a sequence of strings with the parameters used in the SQL expression (i.e., the n tokens in the expression). The number of parameters in the result sequence will exactly match the number of n tokens in the query expression associated with the IQueryCondition.

Parameters

queryParameters A reference to a sequence of strings that will be used to store the parameters used in the SQL expression

Returns

Return codes are:

DDS.ReturnCode Ok - The existing set of query parameters applied to this IQueryCondition has successfully been copied into the specified queryParameters parameter.
DDS.ReturnCode Error - An internal error has occurred.
DDS.ReturnCode AlreadyDeleted - The IQueryCondition has already been deleted.

◆ SetQueryParameters()

ReturnCode DDS.IQueryCondition.SetQueryParameters ( params string [] queryParameters )

This operation changes the query parameters associated with the IQueryCondition.

This operation changes the query parameters associated with the IQueryCondition. The parameter queryParameters is a sequence of strings which are the parameter values used in the SQL query string (i.e., the n tokens in the expression). The number of values in queryParameters must be equal or greater than the highest referenced n token in the queryExpression (e.g. if %1 and %8 are used as parameter in the queryExpression, the queryParameters should at least contain n+1 = 9 values).