I'm confused on how to get my GroupingStore to query the webserver.

Code:
MyApp.grids.RelationshipMemberGrid = Ext.extend(Ext.grid.GridPanel, {
    autoHeight: true,
    iconCls: 'icon-grid',
    title: 'Relationship Members',
    frame: true,
    viewConfig: { forceFit: true },
    relationshipId: null,
    documentId: null,

    initComponent: function () {
        if (this.verifyParameters()) {
            // Initiate functionality
            this.columns = this.buildColumns();
            this.view = this.buildView();
            this.store = this.buildStore();
        }

        MyApp.grids.RelationshipMemberGrid.superclass.initComponent.call(this);
    },

    verifyParameters: function () {
        if (this.relationshipId == null || this.relationshipId < 1) {
            Ext.MessageBox.alert('Error', 'Relationship Id is not valid');
            return false;
        }

        if (this.documentId == null || this.documentId < 1) {
            Ext.MessageBox.alert('Error', 'Document Id is not valid');
            return false;
        }

        return true;
    },

    buildColumns: function () {
        return [{
            header: 'Id',
            dataIndex: 'Id',
            sortable: true,
            width: 10
        }, {
            header: 'Type',
            dataIndex: 'ObjType',
            sortable: true,
            width: 10
        }, {
            header: 'Name',
            dataIndex: 'Name',
            sortable: true
        }];
    },

    buildView: function () {
        return new Ext.grid.GroupingView({
            forceFit: true,
            groupTextTpl: '{text} ({[values.rs.length]} {[values.rs.length > 1 ? "Members" : "Member"]})'
        });
    },

    buildStore: function () {
        return new Ext.data.GroupingStore({
            url: MyAppUrls.ListRelationshipMembers,
            params: { relationshipId: this.relationshipId },
            fields: ['Id', 'ObjType', 'Name'],
            sortInfo: { field: 'Name', direction: 'ASC' },
            groupField: 'ObjType'
        });
    }
});
No javascript errors seem to occur but no http calls are made. The MyAppUrls.ListRelationshipMembers contains a valid string with the correct URL.