/**
* Determine the schema of the output. inferSchema is called on the coordinator instance during query planning and
* may be called several times as the planner gets its act together. It will always be called with the same inputs
* for the same query. This function must behave deterministically, but the shape of the output may vary based on
* inputs and parameters.
* @param schemas all of the schemas of the input arrays (if the operator accepts any)
* @param query the query context
* @return the schema of the outpt, as described above.
*/
ArrayDesc inferSchema(vector< ArrayDesc> schemas, shared_ptr< Query> query)
{
/*
* Make one string attribute: id=0, name="instance_status" of type string, no flags, no default compression.
* The ID of the attribute is simply a number from 0 to num_attributes-1 and must equal to its position
* in the attributes vector.
*/
AttributeDesc outputAttribute (0, "instance_status", TID_STRING, 0, 0);
Attributes outputAttributes(1, outputAttribute);
/* Add the empty tag attribute. Arrays with the empty tag are "emptyable" meaning that some cells may be empty.
* It is a good practice to add this to every constructed array. In fact, in the future it may become the
* default for all arrays.
*/
outputAttributes = addEmptyTagAttribute(outputAttributes);
/* The output dimension: from 0 to "*" with a chunk size of 1. The amount of data returned is so small that the
* chunk size is not relevant.
*/
DimensionDesc outputDimension("instance_no", 0, MAX_COORDINATE, 1, 0);
Dimensions outputDimensions(1, outputDimension);
/* The first argument is the name of the returned array. */
return ArrayDesc("hello_instances", outputAttributes, outputDimensions);
}
/* inferSchema helps the query planner decide on the shape of
* the output array. All operators must define this function.
*/
ArrayDesc inferSchema(vector< ArrayDesc> schemas, shared_ptr< Query> query)
{
ArrayDesc const& matrix = schemas[0];
if(matrix.getAttributes(true)[0].getType() != TID_STRING)
throw SYSTEM_EXCEPTION(SCIDB_SE_INTERNAL, SCIDB_LE_ILLEGAL_OPERATION) << "cu requires a single string-valued attribute";
Attributes outputAttributes(matrix.getAttributes());
Dimensions outputDimensions(matrix.getDimensions());
return ArrayDesc(matrix.getName(), outputAttributes, outputDimensions);
}
