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CHAPTER 8 s BUSINESS OBJECT IMPLEMENTATION
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Since the collection is normally read-only, the IsReadOnly property is set to false before loading the data and then restored to true once the data has been loaded. The result is a fully populated name/value list containing the data from the Roles table in the database. This completes the Project object family, including all collaboration objects. Next, I ll walk briefly through the Resource object family.
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The other primary root object in the object model is Resource. Like Project, a Resource object can be directly created, retrieved, or updated. It also contains a list of child objects. Since I ve already walked through the creation of an editable root business object in detail, there s no need to do the same for the Resource class. However, there are two primary areas of difference that should be discussed. Where the Projects table uses a uniqueidentifier as a primary key, the Resources table uses an int identity column. This means that the database is responsible for assigning the primary key value for any new Resource objects. Additionally, just to show how it is done, I have implemented the Resource, ResourceAssignments, and ResourceAssignment objects to share a common database connection. Where every object in the Project family opens and closes its own database connection, the objects in the Resource family pass a common SqlConnection object between them when doing data access. While this complicates the code somewhat, it may offer some minor performance gains. You can choose the approach that best fits your needs.
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Many databases are designed to use identity columns, where the database is responsible for assigning primary key values to rows of data as they are inserted. While the Guid approach used in Project is somewhat simpler to implement, Resource illustrates how to work with identity columns. The changes are limited to the Data Access region of the code, and in particular the DataPortal_ Insert() method. Where the updateResource stored procedure simply returns the updated timestamp for the row, addResource also returns the newly created identity value: SELECT Id, LastChanged FROM Resources WHERE Id=SCOPE_IDENTITY() This means DataPortal_Insert() needs to retrieve that value and update the object s _id field: [Transactional(TransactionalTypes.TransactionScope)] protected override void DataPortal_Insert() { using (SqlConnection cn = new SqlConnection(Database.PTrackerConnection)) { cn.Open(); using (SqlCommand cm = cn.CreateCommand()) { cm.CommandType = CommandType.StoredProcedure; cm.CommandText = "addResource"; cm.Parameters.AddWithValue("@id", _id); cm.Parameters.AddWithValue("@lastName", _lastName); cm.Parameters.AddWithValue("@firstName", _firstName); SqlParameter param = new SqlParameter("@newId",SqlDbType.Int); param.Direction = ParameterDirection.Output; cm.Parameters.Add(param);
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CHAPTER 8 s BUSINESS OBJECT IMPLEMENTATION
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param = new SqlParameter("@newLastChanged", SqlDbType.Timestamp); param.Direction = ParameterDirection.Output; cm.Parameters.Add(param); cm.ExecuteNonQuery(); _id = (int)cm.Parameters["@newId"].Value; _timestamp = (byte[])cm.Parameters["@newLastChanged"].Value; } // update child objects _assignments.Update(cn, this); } } The method opens the database connection and sets up the SqlCommand object. When the command is executed, it returns both the @newId and @newLastChanged column values, which are used to set the _id and _timestamp fields in the object. The result is that the Resource object s Id property reflects the value assigned by the database as soon as the data is added to the database. Notice that the child objects are updated after this value has been retrieved, which means that all the child ResourceAssignment objects will have access to their parent object s Id value. This is important since they use this value as a foreign key.
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Sharing a Database Connection
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If you look at the preceding DataPortal_Insert() method, you ll notice that the child object collection s Update() method is called before the database connection is closed. In fact, the SqlConnection object is passed as a parameter to the Update() method along with a reference to the Resource object itself: _assignments.Update(cn, this); The idea behind this is to make the connection available to the child objects so a connection doesn t have to be opened and closed for each object. The .NET Framework provides database connection pooling, so talking about opening and closing database connections isn t really meaningful. Just because your code closes or disposes a SqlConnection object doesn t mean the connection is actually closed; in fact, it usually isn t closed, but rather is simply returned to the connection pool for later reuse. What this means is that it typically isn t worth worrying about the frequency of opening and closing the database connection, since your code is really just reusing an already open connection anyway. But if you want to eke out that tiny extra bit of performance, you may want to share the connection. Also, if you are implementing manual ADO.NET transactions, you ll want to follow the flow of code I m showing here; though you would pass the SqlTransaction object as a parameter rather than the SqlConnection object. SqlTransaction objects contain a reference to the underlying SqlConnection, so passing a SqlTransaction provides all the information needed to initialize SqlCommand objects to use the same connection and transaction. The principle remains consistent, however. The Update() method in ResourceAssignments accepts the open SqlConnection object and passes it to each ResourceAssignment child object s data access method: internal void Update(SqlConnection cn, Resource resource) { this.RaiseListChangedEvents = false; // update (thus deleting) any deleted child objects
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