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DataPortal_Insert
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The DataPortal_Insert() method handles the case in which a new object needs to insert its data into the database. It is invoked by the data portal as a result of the UI calling the object s Save() method when the object s IsNew property is true. As with all the methods that change the database, this one is marked with the [Transactional()] attribute to ensure that the code is transactionally protected: [Transactional(TransactionalTypes.TransactionScope)] protected override void DataPortal_Insert() { using (SqlConnection cn = new SqlConnection(Database.PTrackerConnection)) { cn.Open(); using (SqlCommand cm = cn.CreateCommand()) { cm.CommandText = "addProject"; DoInsertUpdate(cm); } } // update child objects _resources.Update(this); } As with DataPortal_Fetch(), this method opens a connection to the database and creates a SqlCommand object. However, it turns out that both the addProject and updateProject stored procedures take almost the same set of parameters. To consolidate code, a DoInsertUpdate() helper method is called to load the common parameters and to execute the SqlCommand object. That method looks like this:
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private void DoInsertUpdate(SqlCommand cm) { cm.CommandType = CommandType.StoredProcedure; cm.Parameters.AddWithValue("@id", _id); cm.Parameters.AddWithValue("@name", _name); cm.Parameters.AddWithValue("@started", _started.DBValue); cm.Parameters.AddWithValue("@ended", _ended.DBValue); cm.Parameters.AddWithValue("@description", _description); SqlParameter param = new SqlParameter("@newLastChanged", SqlDbType.Timestamp); param.Direction = ParameterDirection.Output; cm.Parameters.Add(param); cm.ExecuteNonQuery(); timestamp = (byte[])cm.Parameters["@newLastChanged"].Value; } The DataPortal_Insert() method already set the stored procedure name on the SqlCommand object, so this helper method only needs to add parameters to the object, loading it with the object s data. It then executes the stored procedure. Recall from 6 that both the addProject and updateProject stored procedures perform a SELECT statement to return the updated LastChanged column value. This value is read as a result of the stored procedure call so that the object can update the _timestamp field with the new value from the database. As with DataPortal_Fetch(), the object needs to have the current value of the timestamp for any future updates to the database. Back in DataPortal_Insert(), once the insert operation is complete, the Project object s data is in the database. However, a Project contains child objects, and their data must be added to the database as well. This is handled by calling an Update() method on the child collection object: _resources.Update(this); This method is scoped as internal and is intended for use only by the Project object. It loops through all the child objects in the collection, inserting each one into the database. You ll see the code for this Update() method later in the chapter. Once DataPortal_Insert() is complete, the data portal automatically invokes the MarkOld() method on the object, ensuring that the IsNew and IsDirty properties are both false. Since the object s primary key value in memory now matches a primary key value in the database, it is not new; and since the rest of the object s data values match those in the database, it is not dirty.
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DataPortal_Update
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The DataPortal_Update() method is very similar to DataPortal_Insert(), but it is called by the data portal in the case that IsNew is false. It too opens a database connection and creates a SqlCommand object, and then calls DoInsertUpdate() to execute the updateProject stored procedure: [Transactional(TransactionalTypes.TransactionScope)] protected override void DataPortal_Update() { if (base.IsDirty) { using (SqlConnection cn = new SqlConnection(Database.PTrackerConnection)) { cn.Open(); using (SqlCommand cm = cn.CreateCommand())
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{ cm.CommandText = "updateProject"; cm.Parameters.AddWithValue("@lastChanged", _timestamp); DoInsertUpdate(cm); } } } // update child objects _resources.Update(this); } However, the updateProject stored procedure requires one extra parameter not required by addProject: the timestamp value for the LastChanged column: cm.Parameters.AddWithValue("@lastChanged", _timestamp); This is required for the first-write-wins optimistic concurrency implemented by the stored procedure. The goal is to ensure that multiple users can t overwrite each other s changes to the data. Other than adding this one extra parameter to the SqlCommand object, the DataPortal_Update() method is very similar to DataPortal_Insert().
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