ENH: Support for COUNT queries.

src/Caosdb.m

@@ -123,6 +123,7 @@ classdef Caosdb < handle
     % Execute a query
     %
     % entities = Caosdb.query("FIND Record Foo WITH bar=baz")
+    % entities = Caosdb.query("COUNT Record Foo WITH bar=baz")
     %
     % Parameters
     % ----------
@@ -133,7 +134,7 @@ classdef Caosdb < handle
     % Returns
     % -------
     % entities : cell array
-    %  The retrieved entities.
+    %  The retrieved entities.  If the query was a COUNT query, the result is an int64 instead.
     function entities = query(obj, query_str)
       % Ensure that QUERY is a string.
       assert(ischar(query_str), "maox:InvalidArgument", "QUERY must be a string, was:\n%s", ...
@@ -142,8 +143,11 @@ classdef Caosdb < handle
       % disp("query:");
       % disp(query_str);
       try
-        collection = maox_query(obj.connection, query_str);
+        [collection, count_results] = maox_query(obj.connection, query_str);
         entities = maox_convert_collection(collection);
+        if (count_results >= 0)
+          entities = count_results;
+        end
       catch
         % disp("error handling in Caosdb.m");
         % disp(lasterror());

src/private/maox_query.cpp

@@ -19,14 +19,16 @@ using std::string;
  *
  * @details    This function returns the entities as a cell array.
  *
- * @param connection_name A string with the connection name. May be omitted or
- * an empty string.
+ * @param connection_name   A string with the connection name. May be omitted or an empty string.
  *
- * @param query The query string.
+ * @param query         The query string.
  *
- * @return collection A struct with the entities.
+ * @return resultSet    A struct with the entities.
+ *
+ * @return countResult  The result of a COUNT query, is -1 if zero or more than one COUNT queries
+ * were given.
  */
-void mexFunction(int /*nlhs*/, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
+void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
 
   string conn_name;
   string query;
@@ -41,6 +43,14 @@ void mexFunction(int /*nlhs*/, mxArray *plhs[], int nrhs, const mxArray *prhs[])
       mexErrMsgIdAndTxt("maox:TooManyArguments",
                         "Need 2 arguments: connection_name and a query string.");
     }
+    if (nlhs < 2) {
+      mexErrMsgIdAndTxt("maox:InsufficientReturnArguments",
+                        "Need 2 return arguments: resultSet and queryCount.");
+    }
+    if (nlhs > 2) {
+      mexErrMsgIdAndTxt("maox:TooManyReturnArguments",
+                        "Need 2 return arguments: resultSet and queryCount.");
+    }
     if (!mxIsChar(prhs[1])) {
       mexErrMsgIdAndTxt("maox:InvalidArgument", "The second argument must be a string.");
     }
@@ -65,10 +75,11 @@ void mexFunction(int /*nlhs*/, mxArray *plhs[], int nrhs, const mxArray *prhs[])
   auto t_stat = transaction->WaitForIt();
   maoxdb::throwOctExceptionIfError(transaction.get());
   // Status must be OK or GENERIC_TRANSACTION_ERROR now.
-  const auto &results = transaction->GetResultSet();
-  // std::cout << "size: " << results.Size() << std::endl;
 
+  const auto &results = transaction->GetResultSet();
   auto *mxResults = maoxdb::mxFromResultSet(results);
+  auto *mxCountResults = maoxdb::mxScalarINT64(transaction->GetCountResult());
 
   plhs[0] = mxDuplicateArray(mxResults);
+  plhs[1] = mxCountResults;
 }