Reading from and writing to RDBMS

Reading from and writing to RDBMS
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Reading from a database

Support for reading from a database is brought by

Summer.Batch.Infrastructure.Item.Database.DataReaderItemReader<T> class.

This is an all purpose database reader, usable with any rdbms for which a System.Data.Common.DbProviderFactory can be provided.

DataReaderItemReader requires the following properties to be set at initialization time :

ConnectionString : a System.Configuration.ConnectionStringSettings instance; connection string is used to provide all required details needed to connect to a given database. These details are usually being stored in an application XML configuration file;
Query : a string representing the SQL query to be executed against the database; Obviously, only SELECT SQL statements should be used as query in a database reader. Externalizing these SQL queries in a resource file (.resx) is recommended;
RowMapper: instance of a Summer.Batch.Data.RowMapper<out T>, in charge of converting a row from resultset returned by the query execution to a business object of type T.

In addition, if query contains any parameter, one need to supply a Parameter Source (class that implements

Summer.Batch.Data.Parameter.IQueryParameterSource interface).

Supported syntax for query parameters : the query parameters are identified either with ':' or '@' prefix;

Example 6.9. Query parameters supported syntax examples

(both query are valid and equivalent):

select CODE,NAME,DESCRIPTION,DATE from BA_SQL_READER_TABLE_1 
					where CODE = :Code

select CODE,NAME,DESCRIPTION,DATE from BA_SQL_READER_TABLE_1 
					where CODE = @Code

Two implementations of IQueryParameterSource are provided in Summer Batch :

Summer.Batch.Data.Parameter.DictionaryParameterSource: parameters for queries are stored in a dictionary ; matching with query parameters will be done using dictionary entries keys;
Summer.Batch.Data.Parameter.PropertyParameterSource: PropertyParameterSource constructor requires a business object as argument. the query parameters will be filled by the business object properties, matching will be done using the properties names.

The query used in example is

select CODE,NAME,DESCRIPTION,DATE from BA_SQL_READER_TABLE_1

Records are read from BA_SQL_READER_TABLE_1 table, whose DDL is (target database is MS SQL Server) :

CREATE TABLE [dbo].[BA_SQL_READER_TABLE_1]  (
  [IDENTIFIER]	BIGINT	IDENTITY(1,1) NOT NULL,
  [CODE] INT ,
  [NAME] VARCHAR(30) ,
  [DESCRIPTION] VARCHAR(40) ,
  [DATE] DATE
  )
;

Result from this query execution will be stored in the following DatasourceReaderBO business object:

Example 6.10. DataReaderItemReader target business object

using System;

namespace Com.Netfective.Bluage.Business.Batch.Bos
{
    /// <summary>
    /// Entity DatasourceReaderBO.
    /// </summary>
    [Serializable]
    public class DatasourceReaderBO
    {
        /// <summary>
        /// Property Code.
        /// </summary>
        public int? Code { get; set; }

        /// <summary>
        /// Property Name.
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// Property Description.
        /// </summary>
        public string Description { get; set; }

        /// <summary>
        /// Property Date.
        /// </summary>
        public DateTime? Date { get; set; }

    }
}

Mapping between resultset rows and given business object is done by the following RowMapper:

Example 6.11. DataReaderItemReader target business object RowMapper

using Summer.Batch.Data;
using System;

namespace Com.Netfective.Bluage.Business.Batch.Bos.Mappers
{
    /// <summary>
    /// Utility class defining a row mapper for SQL readers.
    /// </summary>
    public static class DatasourceReaderSQLReaderMapper
    {
        /// <summary>
        /// Row mapper for <see cref="DatasourceReaderBO" />.
        /// </summary>
        public static readonly RowMapper<DatasourceReaderBO> RowMapper = 
        (dataRecord, rowNumber) =>
        {
            var wrapper = new DataRecordWrapper(dataRecord);
            return new DatasourceReaderBO
            {
                Code = wrapper.Get<int?>(0),
                Name = wrapper.Get<string>(1),
                Description = wrapper.Get<string>(2),
                Date = wrapper.Get<DateTime?>(3),
            };
        };
    }
}

Now let's review how to configure a database reader. First, the job XML file:

Example 6.12. DataReaderItemReader declaration in the job XML file

<step id="DatasourceReader">
	<chunk item-count="1000">
		<reader ref="DatasourceReader/DatasourceReaderRecord" />
		...
	</chunk>
</step>

Unity configuration:

Example 6.13. Formatted flat file writer - sample unity configuration

/// <summary>
/// Registers the artifacts required to execute the steps (tasklets, readers, writers, etc.)
/// </summary>
/// <param name="container">the unity container to use for registrations</param>
public override void LoadArtifacts(IUnityContainer container)
{
    ConnectionStringRegistration.Register(container);
    RegisterDatasourceReader(container);
}

/// <summary>
/// Registers the artifacts required for step DatasourceReader.
/// </summary>
/// <param name="container">the unity container to use for registrations</param>
private void RegisterDatasourceReader(IUnityContainer container)
{
	//Connection string
	var readerConnectionstring = 
		System.Configuration.ConfigurationManager.ConnectionStrings["ReaderConnection"];

    // Reader - DatasourceReader/DatasourceReaderRecord
    container.StepScopeRegistration<IItemReader<DatasourceReaderBO>,
    	DataReaderItemReader<DatasourceReaderBO>>("DatasourceReader/DatasourceReaderRecord")
        .Property("ConnectionString").Instance(readerConnectionstring)
        .Property("Query").Value(SqlQueries.DatasourceReader_SQL_QUERY)
        .Property("RowMapper").Instance(DatasourceReaderSQLReaderMapper.RowMapper)
        .Register();

		// ... Processor and writer registration not being shown here

Note

In this example, the connection string is read from the default application configuration file, using System.Configuration.ConfigurationManager. Here is the corresponding XML configuration (points at a MS SQL Server database):

<?xml version="1.0" encoding="utf-8" ?>
<connectionStrings>
  <add name="ReaderConnection"
   providerName="System.Data.SqlClient"
   connectionString="Data Source=(LocalDB)\v11.0;
   	 AttachDbFilename=|DataDirectory|\data\BA_SQL_Reader.mdf;Integrated Security=True" />
</connectionStrings>

The query is read into a resource file (SqlQueries.resx); SqlQueries class is the corresponding designer artifact created by Visual Studio to wrap the underlying resource.

Writing to a database

Summer.Batch.Infrastructure.Item.Database.DatabaseBatchItemWriter<T> is able to write a collection of business objects to the target database, using a INSERT or UPDATE SQL statement.

The following properties must be set at initialization time:

ConnectionString : a System.Configuration.ConnectionStringSettings instance; connection string is used to provide required details needed to connect to a given database. These details are usually being stored in an application XML configuration file;
Query : a string representing SQL query to be executed on the database; To write to a database, only INSERT or UPDATE SQL statements should be used. Externalizing SQL queries in a resource file (.resx) is recommended; As for reader, query parameters will be prefixed either by ':' or '@'.
DbParameterSourceProvider : a class that implements Summer.Batch.Data.Parameter.IQueryParameterSourceProvider<in T> interface, in charge of filling query parameters with appropriate values, usually from a business object.
The method to be implemented is
IQueryParameterSource CreateParameterSource(T item) : query parameters will be fed by consuming Summer.Batch.Data.Parameter.IQueryParameterSource.

Summer Batch provides an implementation for IQueryParameterSourceProvider interface :

Summer.Batch.Data.Parameter.PropertyParameterSourceProvider<in T>

Given an business object of type T, this class will provide a Summer.Batch.Data.Parameter.PropertyParameterSource that maps query parameters to the business object properties, on a naming convention basis.

An extra property can be used to refine the writer behavior :

AssertUpdates : a flag to indicate whether to check if database rows have actually been updated; defaults to true (Recommended mode);

Our writer will be using the following query

INSERT INTO BA_SQL_WRITER_TABLE (CODE,NAME,DESCRIPTION,DATE) 
			VALUES (:code,:name,:description,:date)

, that will write records into the BA_SQL_WRITER_TABLE whose DDL -- for MS SQL Server -- is

CREATE TABLE [dbo].[BA_SQL_WRITER_TABLE]  (
  [IDENTIFIER]	BIGINT	IDENTITY(1,1) NOT NULL,
  [CODE] INT ,
  [NAME] VARCHAR(30) ,
  [DESCRIPTION] VARCHAR(40) ,
  [DATE] DATE
  )
;

Each row written will correspond to an instance of the following business object

Example 6.14. DatabaseBatchItemWriter target business object

using System;

namespace Com.Netfective.Bluage.Business.Batch.Datasource.Bos
{
    /// <summary>
    /// Entity DatasourceWriterBO.
    /// </summary>
    [Serializable]
    public class DatasourceWriterBO
    {
        /// <summary>
        /// Property Code.
        /// </summary>
        public int? Code { get; set; }

        /// <summary>
        /// Property Name.
        /// </summary>
        public string Name { get; set; }

        /// <summary>
        /// Property Description.
        /// </summary>
        public string Description { get; set; }

        /// <summary>
        /// Property Date.
        /// </summary>
        public DateTime? Date { get; set; }

    }
}

Eventually, mapping between business object and query parameters is achieved by using a PropertyParameterSourceProvider.

Now, we need to configure the writer; Firstly in job XML file :

Example 6.15. DatabaseBatchItemWriter declaration in the job XML file

<step id="DatasourceWriter">
	<chunk item-count="1000">
		...
		<writer ref="DatasourceWriter/WriteRecodDatasource" />
	</chunk>
</step>

Unity configuration:

Example 6.16. Database batch writer - sample unity configuration

/// <summary>
/// Registers the artifacts required for step DatasourceWriter.
/// </summary>
/// <param name="container">the unity container to use for registrations</param>
private void RegisterDatasourceWriter(IUnityContainer container)
{
	//Connection string
	var writerConnectionstring = 
		System.Configuration.ConfigurationManager.ConnectionStrings["WriterConnection"];

    //... reader and processor registration not shown here

    // Writer - DatasourceWriter/WriteRecodDatasource
    container.StepScopeRegistration<IItemWriter<DatasourceWriterBO>,
    		DatabaseBatchItemWriter<DatasourceWriterBO>>("DatasourceWriter/WriteRecodDatasource")
        .Property("ConnectionString").Instance(writerConnectionstring)
        .Property("Query").Value(SqlQueries.WriteRecodDatasource_S01_DatasourceWriter_SQL_QUERY)
        .Property("DbParameterSourceProvider")
        	.Reference<PropertyParameterSourceProvider<DatasourceWriterBO>>()
        .Register();
}

	Note
	As in the database reader example: Connection details are read from an application XML config file; Query is read from a resource file (.resx);

Database Support

Summer Batch currently supports following three RDBMS:

RDBMS	Provider Names
Microsoft® SQL Server	`System.Data.SqlClient`
Oracle® Database	`System.Data.OracleClient`, `Oracle.ManagedDataAccess.Client`, `Oracle.DataAccess.Client`
IBM® DB2	`IBM.Data.DB2`

Summer.Batch.Data.IDatabaseExtension interface allows extending Summer Batch to support more RDBMS or provider names. Implementations of this interface present in a referenced assembly will automatically be detected and registered. It has three properties that require a getter:

ProviderNames: An enumeration of the invariant provider names supported by this extension.
PlaceHolderGetter: An instance of IPlaceHolderGetter is used to replace parameters in queries with placeholders. All SQL queries should use either “@” or “:” to prefix parameters, the placeholder getter will be used to transform the query so that it uses placeholders required by the provider.
Incrementer: An instance of IDataFieldMaxValueIncrementer is used to retrieve unique ids for different batch entities, such as job or step executions. Best way to generate unique ids is dependent on the specified RDBMS, thus the extension is required to provide an incrementer.

The following example show how to add support for PostgreSQL using Npgsql provider:

Example 6.17. Adding support for other RDBMS : the PostgreSQL example

public class PostgreSqlExtension : IDatabaseExtension
{
    public IEnumerable<string> ProviderNames
    {
        get { return new[] { "Npgsql" }; }
    }

    public IPlaceholderGetter PlaceholderGetter
    {
        get { return new PlaceholderGetter(name => ":" + name, true); }
    }

    public IDataFieldMaxValueIncrementer Incrementer
    {
        get { return new PostgreSqlIncrementer(); }
    }
}

public class PostgreSqlIncrementer : AbstractSequenceMaxValueIncrementer
{
    protected override string GetSequenceQuery()
    {
        return string.Format("select nextval('{0}')", IncrementerName);
    }
}

In addition to providing a complete support for an additional RDBMS, job repository DDL's should be adapted to the targeted RDBMS.

Some required DDL adjustments are:

adapting types names to RDBMS types (BIGINT vs NUMBER, etc.)
adapting sequence support mechanisms (which are very RDBMS dependant)

	Caution
	We do NOT officially support PostgreSQL in Summer Batch, but for the additional RDBMS support, examples are provided in corresponding appendix section, DDL scripts for PostgreSQL.