Check for layer compatibility - QGIS

field_comparision_qgis

def checkForTransectizerLayer(self, selectedByCombo = True):
        """
        This slto checks if a layer is appropiate for woriking with
        Transectizer. A such layer should have the following
        Attributes:
        ===========
        survey(string, 20): A descripive name of survey/transect.
        station:(string, 10): A short descriptive prefix/name for the stations.
        stnnum(int): Sequential/arbitrary number for the station.
        stnlat(double): Latitude, , in decimal degrees, for the station.
        stnlon(double): Longitude, in decimal degrees, for the station.
        stnobs(string, 254): Observations/remarks for the station.
        
        Checking a layer is done field by field, against a field list
        """
        
        # Creating the list of fields to be compared
        surveyField = QgsField(name = 'survey', type = 10,\
            typeName = 'string', len = 20)
        stationField = QgsField(name = 'station', type = 10,\
            typeName = 'string', len = 10)
        stnnumField = QgsField(name = 'stnnum', type =2,\
            typeName = 'integer', len = 10, prec = 0)
        stnlatField = QgsField(name = 'stnlat', type = 6,\
            typeName = 'double', len = 20, prec = 5)
        stnlonField = QgsField(name = 'stnlon', type = 6,\
            typeName = 'double', len = 20, prec = 5)
        stnobsField = QgsField(name = 'stnobs', type = 10,\
            typeName = 'string', len = 254)
        
        fieldList = (surveyField, stationField, stnnumField,\
            stnlatField, stnlonField, stnobsField)
        
        # Now we get the fields from the layer to be checked
        layerName = self.dlg.ui.layersCombo.currentText()
        layer = QgsMapLayerRegistry.instance().mapLayersByName(layerName)[0]
        provider = layer.dataProvider()
        fieldsToCheck = provider.fields()
        
        # A valid layer for the transectizer will have ALL of the defined
        # fields. Direct comparation on fields is possible.
        layerOK = all(field in fieldsToCheck for field in fieldList)
       
        
        # Time to manage the results of the field tests
        msg = QMessageBox() 
        
        # If our layer is compatible with transectizer (it has all the
        # required fields), we just return it
        if layerOK:
            if selectedByCombo:
                msg.setText(self.tr("<center>%s is a valid layer<br>for Transectizer to work<center>" %layerName))
                msg.exec_()
            return layer
        # If not, we offer the user the chance
        # of creating them in the chosen layer
        else:
            msg.setText(self.tr("""<center>It looks like the selected layer<br>
                has not the fields required for Transectizer to work.<br>
                Do you want them to be added to your layer?<center>"""))
            btn1 = msg.addButton(self.tr("Add and continue"), QMessageBox.YesRole)
            btn2 = msg.addButton(self.tr("Cancel"), QMessageBox.NoRole)
            msg.exec_()
            # Creation of the new fields in the layer
            if msg.clickedButton() == btn1:
                layer.startEditing()
                layer.dataProvider().addAttributes(fieldList)
                layer.commitChanges()
                layer.reload()
                return layer
            else:
                return False