Introduction

This page tells you how to build a simple model using the NavWin MVP Framework. The framework comes with a simple way to serialise your data and also to read it and save it to a text file. The MVP does not use .NET serialisation because we do not want to process the complete model data on every server call back. The MVP model is ‘process-on-demand.’

Top level class

A model for an application has a single top level class which inherits the NWModel base class. The model base class provides four pre-defined functions for reading and writing the data. Unless you are using your own data source, then you do not need to do anything with these functions. They are invoked automatically when needed.  In addition, the model inherits NWModelObject which means the model is itself an object. Implement the abstract methods, but leave them empty for now

public class ModelMyApp : NWModel {     public override void SetStructure()     {     }       public override void GetStructure()     {     } }

Model objects

The model is made up of a collection of objects which inherit NWModelObject. Note, in the very simple case, only one model object is needed and that is the model itself (as this inherits NWModelObject). If you need more than one object class in your model then declare it like this

public class ModelMyExtraModelClass : NWModelObject {     public override void SetStructure()     {     }       public override void GetStructure()     {     } }

The model object creator

Every model object needs to declare a generic type called NWModelObjectCreator<>. This provides some powerful functions that are generic in function but specific to each type. You will see the functions allow you to write very concise code when creating objects.

public class ModelMyObject : NWModelObject {    internal static NWModelObjectCreator<ModelMyObject> Creator = new NWModelObjectCreator<ModelMyObject>(); }

 

Getting and setting scalar properties

Scalar properties are easy to deal with. Simply declare a public field (or use can use get/set properties) and these can be loaded and saved directly using code like the following. The example below will read and write a single string field called Name. Note that we directly access a protected variable _objStruct which maintains an internal representation of the object.

public class ModelMyObject : NWModelObject {     public string Name;       public override void SetStructure()     {         this.Name = _objStruct.GetString("Name");     }     public override void GetStructure()     {         _objStruct.SetString("Name", this.Name); }                                   }

Getting and setting a list of scalar values

The framework also supports the idea that you want to store list of scalar values (which all have the same type).

As usual, the list is only processed if it is accessed. The following code demonstrates how to use a list of scalar values.

public class ModelMyObject : NWModelObject {     public List<string> _names = null;       public override void SetStructure()     {         // no action needed – load on demand     }     public override void GetStructure()     {         _objStruct.SetList("Names",_names); }     public List<string> Names     {         get         {             return _objStruct.PropertyGetList("Names", ref _names);         } } }

 

 

Getting and setting a reference to an NW object

So long as you are dealing with an object that is derived from NWModelObject then you can make a reference to the object and this reference is automatically stored. Note that the object unique ID is stored. The specific object being referenced has its own database entry so the whole framework supports multiple references to the same object and, more generally, recursion.

public class ModelMyApp : NWModel {     private ModelMyObject _myObject = null;       public override void SetStructure()     {         // no action needed – load on demand     }       public override void GetStructure()     {         _objStruct.SetObject("MyObject", _myObject);     }     public ModelMyObject MyObject     {         get         {             return ModelMyObject.Creator.PropertyGetObject("MyObject ", _objStruct, ref _myObject);           }         set         {             ModelMyObject.Creator.PropertySetObject(ref _myObject, value);     } }

 

Getting and setting lists of NW objects

So long as you are dealing with objects that are derived from NWModelObject then you can set up a list of these objects which will be stored in the database. In the database, you only store the list of unique object ID’s. The structure shown below means it is necessary to only process the list of objects in the event that this list is actually needed. If the list is never needed then the list and the underlying objects will never be processed.

public class ModelMyApp : NWModel {     private List<ModelMyObject> _myList = null;       public override void SetStructure()     {         // no action needed – load on demand     }       public override void GetStructure()     {         ModelMyObject.Creator.SetListObject(_objStruct, "List", _myList);     }     public List< ModelMyObject> MyList     {         get         {             return ModelMyObject.Creator.PropertyGetObjectList("List", _objStruct, ref _myList);         }       }

 

Model Is Dirty

Although the model provides functions to read and write data and serialize the data (get and set) your code is not expected to call these functions directly. You can override them (e.g. in order to write to your own custom database and not a text file) however you should not call them. In order to tell the framework to save the current model, you should set the following flag at the end of any changes you want to save

_model.NWIsDirty = true;

 

This simply tells the framework that the date has changed and needs to be saved. The framework will either save the data to the server or send it to the client to be saved as local data.