Support for adding empty datasets (closes #47)

resources/packages/common/data.json

@@ -167,6 +167,46 @@
                     }
                 ]
             }, 
+            {
+                "format": [
+                    {
+                        "lspace": true, 
+                        "rspace": true, 
+                        "type": "const", 
+                        "value": "CREATE"
+                    }, 
+                    {
+                        "lspace": true, 
+                        "rspace": true, 
+                        "type": "const", 
+                        "value": "EMPTY"
+                    }, 
+                    {
+                        "lspace": true, 
+                        "rspace": true, 
+                        "type": "const", 
+                        "value": "DATASET"
+                    }, 
+                    {
+                        "lspace": true, 
+                        "rspace": true, 
+                        "type": "var", 
+                        "value": "name"
+                    }
+                ], 
+                "id": "empty", 
+                "name": "Empty Dataset", 
+                "parameter": [
+                    {
+                        "datatype": "string", 
+                        "hidden": false, 
+                        "id": "name", 
+                        "index": 0, 
+                        "name": "Dataset Name", 
+                        "required": true
+                    }
+                ]
+            }, 
             {
                 "format": [
                     {

vizier/engine/packages/vizual/base.py

@@ -31,6 +31,7 @@
 VIZUAL_INS_COL = 'insertColumn'
 VIZUAL_INS_ROW = 'insertRow'
 VIZUAL_LOAD = 'load'
+VIZUAL_EMPTY_DS = 'empty'
 VIZUAL_UNLOAD = 'unload'
 VIZUAL_MOV_COL = 'moveColumn'
 VIZUAL_MOV_ROW = 'moveRow'

vizier/engine/packages/vizual/processor.py

@@ -28,6 +28,8 @@
 import vizier.engine.packages.vizual.api.base as apibase
 from vizier.api.webservice import server
 from vizier.config.app import AppConfig
+import vizier.mimir as mimir
+from vizier.datastore.mimir.dataset import MimirDatasetColumn
 
 """Property defining the API class if instantiated from dictionary."""
 PROPERTY_API = 'api'
@@ -105,6 +107,11 @@ def compute(self, command_id, arguments, context):
                 args=arguments,
                 context=context
             )
+        elif command_id == cmd.VIZUAL_EMPTY_DS:
+            return self.compute_empty_dataset(
+                args=arguments,
+                context=context
+            )
         elif command_id == cmd.VIZUAL_UNLOAD:
             return self.compute_unload_dataset(
                 args=arguments,
@@ -465,6 +472,71 @@ def compute_load_dataset(self, args, context):
                 resources=result.resources
             )
         )
+
+    def compute_empty_dataset(self, args, context):
+        """Execute empty dataset command.
+
+        Parameters
+        ----------
+        args: vizier.viztrail.command.ModuleArguments
+            User-provided command arguments
+        context: vizier.engine.task.base.TaskContext
+            Context in which a task is being executed
+
+        Returns
+        -------
+        vizier.engine.task.processor.ExecResult
+        """
+        outputs = ModuleOutputs()
+        default_columns = [ ("''", "unnamed_column") ]
+        ds_name = args.get_value(pckg.PARA_NAME).lower()
+        if ds_name in context.datasets:
+            raise ValueError('dataset \'' + ds_name + '\' exists')
+        if not is_valid_name(ds_name):
+            raise ValueError('invalid dataset name \'' + ds_name + '\'')
+        try:
+            source = "SELECT {};".format(", ".join(
+                            default_val + " AS " + col_name
+                            for default_val, col_name in default_columns
+                        ))
+            view_name = mimir.createView(
+                dict(),
+                source
+            )
+
+            columns = [
+                MimirDatasetColumn(
+                    identifier=col_id,
+                    name_in_dataset=col_defn[1]
+                )
+                for col_defn, col_id in zip(default_columns, range(len(default_columns)))
+            ]
+
+            ds = context.datastore.register_dataset(
+                table_name=view_name,
+                columns=columns,
+                row_counter=1
+            )
+            provenance = ModuleProvenance(
+                write={
+                    ds_name: DatasetDescriptor(
+                        identifier=ds.identifier,
+                        columns=ds.columns,
+                        row_count=ds.row_count
+                    )
+                }
+            )
+            outputs.stdout.append(TextOutput("Empty dataset '{}' created".format(ds_name)))
+        except Exception as ex:
+            provenance = ModuleProvenance()
+            outputs.error(ex)
+        return ExecResult(
+            is_success=(len(outputs.stderr) == 0),
+            outputs=outputs,
+            provenance=provenance
+        )
+
+
 
     def compute_unload_dataset(self, args, context):
         """Execute unload dataset command.

vizier/viztrail/module/output.py

@@ -56,10 +56,13 @@ def format_stack_trace(ex):
         )
         for element in trace
     ])
-    trace = (
-        ["  ... caused by "+trace[0]]+
-        ["  ... called by "+line for line in trace[1:]]
-    )
+    if len(trace) > 0:
+        trace = (
+            ["  ... caused by "+trace[0]]+
+            ["  ... called by "+line for line in trace[1:]]
+        )
+    else:
+        return "INTERNAL ERROR\n{}".format(ex)
     return "{}".format("\n".join(trace))
 
 
@@ -137,6 +140,9 @@ def error(self, ex):
                     message = message + ":\n " + str(traceback.format_exc())
         except Exception as e:
             message = template.format(type(e).__name__, e.args)
+            if debug_is_on():
+                message += "\n"+format_stack_trace(e)
+
         self.stderr.append(TextOutput(message))
         return self