Each database vendor is associated with a particular implementation of the IDbProvider interfaces. A variety of implementations are provided with Spring such as SqlServer, Oracle and MySql. Refer to the documentation on Spring's DbProvider for creating a configuration for database that is not yet provided. The programmatic way to create an IDbProvider is shown below

IDbProvider dbProvider = DbProviderFactory.GetDbProvider("System.Data.SqlClient");

The Execute method and its associated callback function/inteface is the basic method upon which all the other methods in AdoTemplate delegate their work. If you can not find a suitable 'one-liner' method in AdoTemplate for your purpose you can always fall back to the Execute method to perform any database operation while benefiting from ADO.NET resource management and transaction enlistment. This is commonly the case when you are using special provider specific features, such as XML or BLOB support.

In this example a simple query against the 'Northwind' database is done to determine the number of customers who have a particular postal code.

public int FindCountWithPostalCode(string postalCode)
{
  return adoTemplate.Execute<int>(delegate(DbCommand command)
         {
             command.CommandText =
                 "select count(*) from Customers where PostalCode = @PostalCode";
                                                    
             DbParameter p = command.CreateParameter();
             p.ParameterName = "@PostalCode";
             p.Value = postalCode;
             command.Parameters.Add(p);
                                                         
             return (int)command.ExecuteScalar();

          });

}

The DbCommand that is passed into the anonymous delegate is already has it Connection property set to the corresponding value of the dbProvider instance used to create the template. Furthermore, the Transaction property of the DbCommand is set based on the transactional calling context of the code as based on the use of Spring's transaction management features. Also note the feature of anonymous delegates to access the variable 'postalCode' which is defined 'outside' the anonymous delegate implementation. The use of anonymous delegates is a powerful approach since it allows you to write compact data access code. If you find that your callback implementation is getting very long, it may improve code clarity to use an interfaced based version of the callback function, i.e. an ICommandCallback shown below.

As you can see, only the most relevant portions of the data access task at hand need to be coded. (Note that in this simple example you would be better off using AdoTemplate's ExecuteScalar method directly. This method is described in the following sections). As mentioned before, the typical usage scenario for the Execute callback would involve downcasting the passed in DbCommand object to access specific provider API features.

There is also an interface based version of the execute method. The signatures for the delegate and interface are shown below

public delegate T CommandDelegate<T>(DbCommand command);  


public interface ICommandCallback
{
  T DoInCommand<T>(DbCommand command);
}

While the delegate version offers the most compact syntax, the interface version allows for reuse. The corresponding method signatures on Spring.Data.Generic.AdoTemplate are shown below

public class AdoTemplate : AdoAccessor, IAdoOperations
{
   ...

   T Execute<T>(ICommandCallback action);

   T Execute<T>(CommandDelegate<T> del);

   ...
}

While it is common for .NET 2.0 ADO.NET provider implementations to inherit from the base class System.Data.Common.DbCommand, that is not a requirement. To accomodate the few that don't, which as of this writing are the latest Oracle (ODP) provider and Postgres, two additional execute methods are provided. The only difference is the use of callback and delegate implementations that have IDbCommand and not DbCommand as callback arguments. The following listing shows these methods on AdoTemplate.

public class AdoTemplate : AdoAccessor, IAdoOperations
{
   ...

   T Execute<T>(IDbCommandCallback action);

   T Execute<T>(IDbCommandDelegate<T> del);

   ...
}

where the signatures for the delegate and interface are shown below

public delegate T IDbCommandDelegate<T>(IDbCommand command);


public interface IDbCommandCallback<T>
{
  T DoInCommand(IDbCommand command);
}

AdoTemplate differs from its .NET 2.0 generic counterpart in that it exposes the interface IDbCommand in its 'Execute' callback methods and delegate as compared to the abstract base class DbProvider. Also, since anonymous delegates are not available in .NET 1.1, the typical usage pattern requires you to create a explicitly delegate and/or class that implements the ICommandCallback interface. Example code to query In .NET 1.1 the 'Northwind' database is done to determine the number of customers who have a particular postal code is shown below.

public virtual int FindCountWithPostalCode(string postalCode)
{
  return (int) AdoTemplate.Execute(new PostalCodeCommandCallback(postalCode));
}

and the callback implementation is

private class PostalCodeCommandCallback : ICommandCallback
{
    private string cmdText = "select count(*) from Customer where PostalCode = @PostalCode";

    private string postalCode;
    
    public PostalCodeCommandCallback(string postalCode)
    {
        this.postalCode = postalCode;
    }

    public object DoInCommand(IDbCommand command)
    {
        command.CommandText = cmdText;

        IDbDataParameter p = command.CreateParameter();
        p.ParameterName = "@PostalCode";
        p.Value = postalCode;
        command.Parameters.Add(p);
        
        return command.ExecuteScalar();

    }
}

Note that in this example, one could more easily use AdoTemplate's ExecuteScalar method.

The Execute method has an interface and delegate overloads. The signatures for the delegate and interface are shown below

public delegate object CommandDelegate(IDbCommand command);

public interface ICommandCallback
{
  object DoInCommand(IDbCommand command);
}

The corresponding method signatures on Spring.Data.AdoTemplate are shown below

public class AdoTemplate : AdoAccessor, IAdoOperations
{
   ...

   object Execute(CommandDelegate del);

   object Execute(ICommandCallback action);

   ...

}

Note that you have to cast to the appropriate object type returned from the execute method.

There are many methods in AdoTemplate so it is easy to feel a bit overwhelmed when taking a look at the SDK documentation. However, after a while you will hopefully find the class 'easy to navigate' with intellisence. Here is a quick categorization of the method names and their associated data access operation. Each method is overloaded to handle common cases of passing in parameter values.

The generic 'catch-all' method

The following methods mirror those on the DbCommand object.

Mapping result sets to objects

Mapping result set to a single object

Query with a callback to create the DbCommand object. These are generally used by the framework itself to support other functionality, such as in the Spring.Data.Objects namespace.

DataTable and DataSet operations

Parameter Creation utility methods

In turn each method typically has four overloads, one with no parameters and three for providing parameters. Aside from the DataTable/DataSet operations, the three parameter overloads are of the form shown below

The CallbackInterfaceOrDelegate is one of the three types listed previously. The parameters setting arguments are of the form

The first overload is a convenience method when you only have one parameter to set. The database enumeration is the base class 'Enum' allowing you to pass in any of the provider specific enumerations as well as the common DbType enumeration. This is a trade off of type-safety with provider portability. (Note generic version could be improved to provide type safety...).

The second overload contains a collection of parameters. The data type is Spring's IDbParameters collection class discussed in the following section.

The third overload is a callback interface allowing you to set the parameters (or other properties) of the IDbCommand passed to you by the framework directly. (TODO provide delegate version of ICommandSetter.)

If you are using .NET 2.0 the delegate versions of the methods are very useful since very compact definitions of database operations can be created that reference variables local to the DAO method. This removes some of the tedium in passing parameters around with interface based versions of the callback functions since they need to be passed into the constructor of the implementing class. The general guideline is to use the delegate when available for functionality that does not need to be shared across multiple DAO classes or methods and use interface based version to reuse the implementation in multiple places. The .NET 2.0 versions make use of generics where appropriate and therefore enhance type-safety.

Instead of creating a parameter on one line of code, then setting its type on another and size on another, a builder and parameter interface, IDbParametersBuilder and IDbParameter respectfully, are provided so that this declaration process can be condensed. The IDbParameter support chaining calls to its methods, in effect a simple language-constrained domain specific language, to be fancy about it. Here is an example of it in use.

IDbParametersBuilder builder = CreateDbParametersBuilder();
builder.Create().Name("Country").Type(DbType.String).Size(15).Value(country);
builder.Create().Name("City").Type(DbType.String).Size(15).Value(city);


// now get the IDbParameters collection for use in passing to AdoTemplate methods.


IDbParameters parameters = builder.GetParameters();

Please note that IDbParameters and IDbParameter are not part of the BCL, but part of the Spring.Data.Common namespace. The IDbParameters collection is a frequent argument to the overloaded methods of AdoTemplate.

The parameter prefix, i.e. '@' in Sql Server, is not required to be added to the parameter name. The DbProvider is aware of this metadata and AdoTemplate will add it automatically if required before execution.

An additional of the IDbParametersBuilder is to create a Spring FactoryObject that creates IDbParameters for use in the XML configuration file of the IoC container. By leveraging Spring's expression evaluation language, the above lines of code can be taken as text from the XML configuration file and executed. As a result you can externalize your parameter definitions from your code. In combination with abstract object definitions and importing of configuration files your increase the chances of having one code base support multiple database providers just by a change in configuration files. Explicit support for this functionality will be in the final release.

This class is similar to the parameter collection class you find in provider specific implementations of IDataParameterCollection. It contains a variety of convenience methods to build up a collection of parameters.

Here is an abbreviated listing of the common convenience methods.

Here a simple usage example

// inside method has has local variable country and city...

IDbParameters parameters = CreateDbParameters();
parameters.AddWithValue("Country", country).DbType = DbType.String;
parameters.Add("City", DbType.String).Value = city;


// now pass on to AdoTemplate methods.

The parameter prefix, i.e. '@' in Sql Server, is not required to be added to the parameter name. The DbProvider is aware of this metadata and AdoTemplate will add it automatically if required before execution.

ExecuteNonQuery is used to perform create, update, and delete operations. It has four overloads listed below reflecting different ways to set the parameters.

An example of using this method is shown below

        public void CreateCredit(float creditAmount)
        {
            AdoTemplate.ExecuteNonQuery(CommandType.Text,
                    String.Format("insert into Credits(creditAmount) VALUES ({0})",
                    creditAmount));
        }

TODO

An example of using this method is shown below

int iCount = (int)adoTemplate.ExecuteScalar(CommandType.Text, "SELECT COUNT(*) FROM TestObjects");
                

TODO

The ResultSetExtractor gives you control to iterate over the IDataReader returned from the query. You are responsible for iterating through all the result sets and returning a corresponding result object. Implementations of IResultSetExtractor are typically stateless and therefore reusable as long as the implementation doesn't access stateful resources. The framework will close the IDataReader for you.

The interface and delegate signature for ResutSetExtractors is shown below for the generic version in the Spring.Data.Generic namespace

public interface IResultSetExtractor<T>
{
  T ExtractData(IDataReader reader);
}

public delegate T ResultSetExtractorDelegate<T>(IDataReader reader);

The definition for the non-generic version is shown below

public interface IResultSetExtractor
{
    object ExtractData(IDataReader reader);
}

public delegate object ResultSetExtractorDelegate(IDataReader reader);

Here is an example taken from the Spring.DataQuickStart. It is a method in a DAO class that inherits from AdoDaoSupport, which has a convenience method 'CreateDbParametersBuilder()'.

        public virtual IList<string> GetCustomerNameByCountryAndCityWithParamsBuilder(string country, string city)
        {

            IDbParametersBuilder builder = CreateDbParametersBuilder();
            builder.Create().Name("Country").Type(DbType.String).Size(15).Value(country);
            builder.Create().Name("City").Type(DbType.String).Size(15).Value(city);
            return AdoTemplate.QueryWithResultSetExtractor(CommandType.Text,
                                                           customerByCountryAndCityCommandText,
                                                           new CustomerNameResultSetExtractor<List<string>>(),
                                                           builder.GetParameters());
        }
        

The implementation of the ResultSetExtractor is shown below.

    internal class CustomerNameResultSetExtractor<T> : IResultSetExtractor<T> where T : IList<string>, new()
    {

        public T ExtractData(IDataReader reader)
        {
            T customerList = new T();
            while (reader.Read())
            {
                string contactName = reader.GetString(0);
                customerList.Add(contactName);
            }
            return customerList;
        }
    }

Internally the implementation of the QueryWithRowCallback and QueryWithRowMapper methods are specializations of the general ResultSetExtractor. For example, the QueryWithRowMapper implementation iterates through the result set, calling the callback method 'MapRow' for each row and collecting the results in an IList. If you have a specific case that is not covered by the QueryWithXXX methods you can subclass AdoTemplate and follow the same implementation pattern to create a new QueryWithXXX method to suit your needs.

The RowCallback is usually a statefull object itself or populates another stateful object that is accessible to the calling code. Here is a sample take from the Data QuickStart

    public class RowCallbackDao : AdoDaoSupport
    {
        private string cmdText = "select ContactName, PostalCode from Customers";

        public virtual IDictionary<string, IList<string>> GetPostalCodeCustomerMapping()
        {
            PostalCodeRowCallback statefullCallback = new PostalCodeRowCallback();
            AdoTemplate.QueryWithRowCallback(CommandType.Text, cmdText,
                                             statefullCallback);

            // Do something with results in stateful callback...
            return statefullCallback.PostalCodeMultimap;
        }
             
    }

The PostalCodeRowCallback builds up state which is then retrieved via the property PostalCodeMultimap. The Callback implementation is shown below

    internal class PostalCodeRowCallback : IRowCallback
    {
        private IDictionary<string, IList<string>> postalCodeMultimap =
            new Dictionary<string, IList<string>>();

        public IDictionary<string, IList<string>> PostalCodeMultimap
        {
            get { return postalCodeMultimap; }
        }

        public void ProcessRow(IDataReader reader)
        {
            string contactName = reader.GetString(0);
            string postalCode = reader.GetString(1);
            IList<string> contactNameList;
            if (postalCodeMultimap.ContainsKey(postalCode))
            {
                contactNameList = postalCodeMultimap[postalCode];
            }
            else
            {
                postalCodeMultimap.Add(postalCode, contactNameList = new List<string>());
            }
            contactNameList.Add(contactName);
        }
    }

The RowMapper lets you focus on just the logic to map a row of your result set to an object. The creation of a IList to store the results and iterating through the IDataReader is handled by the framework. Here is a simple example taken from the Data QuickStart application

    public class RowMapperDao : AdoDaoSupport
    {
        private string cmdText = "select Address, City, CompanyName, ContactName, " +
                             "ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
                             "Region from Customers";


        public virtual IList<Customer> GetCustomers()
        {
            return AdoTemplate.QueryWithRowMapper(CommandType.Text, cmdText,
                                                  new CustomerRowMapper<Customer>());
        }
    }

where the implementation of the RowMapper is

    public class CustomerRowMapper<T> : IRowMapper<T> where T : Customer, new()
    {        
        public T MapRow(IDataReader dataReader, int rowNum)
        {
            T customer = new T();
            customer.Address = dataReader.GetString(0);
            customer.City = dataReader.GetString(1);
            customer.CompanyName = dataReader.GetString(2);
            customer.ContactName = dataReader.GetString(3);
            customer.ContactTitle = dataReader.GetString(4);
            customer.Country = dataReader.GetString(5);
            customer.Fax = dataReader.GetString(6);
            customer.Id = dataReader.GetString(7);
            customer.Phone = dataReader.GetString(8);
            customer.PostalCode = dataReader.GetString(9);
            customer.Region = dataReader.GetString(10);
            return customer;
        }
    }

You may also pass in a delegate, which is particularly convenient if the mapping logic is short and you need to access local variables within the mapping logic.

        public virtual IList<Customer> GetCustomersWithDelegate()
        {
            return AdoTemplate.QueryWithRowMapperDelegate<Customer>(CommandType.Text, cmdText,
                        delegate(IDataReader dataReader, int rowNum)
                            {
                                Customer customer = new Customer();
                                customer.Address = dataReader.GetString(0);
                                customer.City = dataReader.GetString(1);
                                customer.CompanyName = dataReader.GetString(2);
                                customer.ContactName = dataReader.GetString(3);
                                customer.ContactTitle = dataReader.GetString(4);
                                customer.Country = dataReader.GetString(5);
                                customer.Fax = dataReader.GetString(6);
                                customer.Id = dataReader.GetString(7);
                                customer.Phone = dataReader.GetString(8);
                                customer.PostalCode = dataReader.GetString(9);
                                customer.Region = dataReader.GetString(10);
                                return customer;
                            });
        }

The QueryForObject method is used when you expect there to be exactly one object returned from the mapping, otherwise a Spring.Dao.IncorrectResultSizeDataAccessException will be thrown. Here is some sample usage taken from the Data QuickStart.

    public class QueryForObjectDao : AdoDaoSupport
    {
        private string cmdText = "select Address, City, CompanyName, ContactName, " +
                     "ContactTitle, Country, Fax, CustomerID, Phone, PostalCode, " +
                     "Region from Customers where ContactName = @ContactName";
        
        public Customer GetCustomer(string contactName)
        {
            return AdoTemplate.QueryForObject(CommandType.Text, cmdText, 
                                              new CustomerRowMapper<Customer>(),
                                              "ContactName", DbType.String, 30, contactName);
        }
    }

TODO

TODO

TODO

TODO

TODO

TODO

The StoredProcedure class allows you to call and extract the results of a stored procedure with very little code. The ability to derive the parameters programmatically and cache them for later results in much less boiler plate code that you have to write. You can of course define the parameters explicitly if you choose to do so.

The methods you can execute on a stored procedure fall into three categories

Each of these methods returns an IDictionary that contains the output parameters and/or any results from Spring's object mapping framework. The arguments to these methods can be a variable length argument list, in which case the order must match the parameter order of the stored procedure, or a IDictionary with parameter key/value pairs. In the latter case the method names are suffixed with the work 'ByNamedParamter'.

Lets take a look at an example. The following stored procedure class will call the CustOrdersDetail stored procedure in the Northwind database, passing in the OrderID as a stored procedure argument and returning a collection of OrderDetails business objects.

    public class CustOrdersDetailStoredProc : StoredProcedure
    {
        private static string procedureName = "CustOrdersDetail";

        public CustOrdersDetailStoredProc(IDbProvider dbProvider) : base(dbProvider, procedureName)
        {           
            DeriveParameters();
            AddRowMapper("orderDetailRowMapper", new OrderDetailRowMapper() );
            Compile();
        }
        
        public virtual IList GetOrderDetails(int orderid)
        {
            IDictionary outParams = Query(orderid);
            return outParams["orderDetailRowMapper"] as IList;
        }

    }

The 'DeriveParameters' method saves you the trouble of having to declare each parameter explicitly. When using DeriveParameters is it often common to use the Query method that takes a variable length list of arguments. This assumes additional knowledge on the order of the stored procedure arguments. If you do not want to follow this loose shorthand convention, you can call the method QueryByNamesParameters instead passing in a IDictionary of parameter key/value pairs.

The StoredProcedure class are threadsafe once 'compiled', an act which is usually done in the constructor. This sets up the cache of database parameters that can be used on each call to Query. The implementation of IRowMapper that is used to extract the business objects is 'registered' with the class and then later retrieved by name as a fictional output parameter. You may also register IRowCallback and IResultSetExtractor callback interfaces via the AddRowCallback and AddResultSetExtractor methods.