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More interesting and complex is the DataPortal_Fetch() method, which is called by the data portal to tell the object that it should load its data from the database (or other data source). The method accepts a Criteria object as a parameter, which contains the criteria data needed to identify the data to load: private void DataPortal_Fetch(Criteria criteria) { using (SqlConnection cn = new SqlConnection(Database.PTrackerConnection)) { cn.Open(); using (SqlCommand cm = cn.CreateCommand()) { cm.CommandType = CommandType.StoredProcedure; cm.CommandText = "getProject"; cm.Parameters.AddWithValue("@id", criteria.Id); using (SafeDataReader dr = new SafeDataReader(cm.ExecuteReader())) { dr.Read(); _id = dr.GetGuid("Id"); _name = dr.GetString("Name"); _started = dr.GetSmartDate("Started", _started.EmptyIsMin); _ended = dr.GetSmartDate("Ended", _ended.EmptyIsMin); _description = dr.GetString("Description"); dr.GetBytes("LastChanged", 0, _timestamp, 0, 8); // load child objects dr.NextResult(); _resources = ProjectResources.GetProjectResources(dr); } } } }
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CHAPTER 8 s BUSINESS OBJECT IMPLEMENTATION
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This method is not marked with either the [RunLocal()] or [Transactional()] attributes. Since it does interact with the database, [RunLocal()] is inappropriate. That attribute could prevent the data portal from running this code on the application server, causing runtime errors when the database is inaccessible. Also, since this method doesn t update any data, it doesn t need transactional protection, and so there s no need for the [Transactional()] attribute. You should also notice that no exceptions are caught by this code. If the requested Id value doesn t exist in the database, the result will be a SQL exception, which will automatically flow back through the data portal to the UI code, contained within a DataPortalException. This is intentional, as it allows the UI to have full access to the exception s details so the UI can decide how to notify the user that the data doesn t exist in the database. The first thing the method does is open a connection to the database: using (SqlConnection cn = new SqlConnection(Database.PTrackerConnection)) { cn.Open(); Database.PTrackerConnection is a call to a helper class in ProjectTracker.Library. This helper simply abstracts the process of retrieving the database connection string. It uses System.Configuration to get the data, and looks like this: public static string PTrackerConnection { get { return ConfigurationManager.ConnectionStrings ["PTracker"].ConnectionString; } } Because the ConfigurationManager is used in this code, a reference to System.Configuration.dll is required by ProjectTracker.Library. This PTrackerConnection property is merely a convenience to simplify the code in business objects. You may use a similar concept in your code if you choose. Then, within a using block, a SqlCommand object is initialized to call the getProject stored procedure: using (SqlCommand cm = cn.CreateCommand()) { cm.CommandType = CommandType.StoredProcedure; cm.CommandText = "getProject"; cm.Parameters.AddWithValue("@id", criteria.Id); Note the use of the criteria parameter. This is the Criteria object that was created in the GetProject() factory method, and so it provides access to the criteria data supplied to the factory method by the UI. The SqlCommand object is then executed to return a data reader: using (SafeDataReader dr = new SafeDataReader(cm.ExecuteReader())) Rather than using a SqlDataReader, this code creates an instance of the Csla.Data.SafeData Reader class. This provides automatic protection from errant null values in the data, and also enables support for the SmartDate data type. The data reader is then used to populate the object s fields like this: _id = dr.GetGuid("Id"); _name = dr.GetString("Name"); _started = dr.GetSmartDate("Started", _started.EmptyIsMin); _ended = dr.GetSmartDate("Ended", _ended.EmptyIsMin); _description = dr.GetString("Description"); dr.GetBytes("LastChanged", 0, _timestamp, 0, 8);
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The SmartDate values are retrieved using the SafeDataReader object s GetSmartDate() method, which automatically handles the translation of null values into appropriate empty date values. Also notice that the LastChanged column is retrieved and placed into the _timestamp byte array. This value is never exposed outside the object, but is maintained for later use if the object is updated. Recall from 6 that LastChanged is a timestamp value in the database table, and is used by the updateProject stored procedure to implement first-write-wins optimistic concurrency. The object must be able to provide updateProject with the original timestamp value that was in the table when the data was first loaded. At this point, the Project object s fields have been loaded. But Project contains a collection of child objects, and they need to be loaded as well. Remember that the getProject stored procedure returns two result sets: the first with the project s data; the second with the data for the child objects. The NextResult() method of the data reader moves to the second result set so the child collection object can simply loop through all the rows, creating a child object for each: dr.NextResult(); _resources = ProjectResources.GetProjectResources(dr); Now that the object contains data loaded directly from the database, it is an old object. The definition of an old object is that the primary key value in the object matches a primary key value in the database. In 4, the data portal was implemented to automatically call the object s MarkOld() method after DataPortal_Fetch() is complete. That ensures that the object s IsNew and IsDirty properties will return false.
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