Mapping

The Mapper make data-access coding simpler and more productive by using property attributes to map a model class’s properties to data values — parameters, reader columns, and (in the case of SQL Server) table-value parameters. This reduces and simplifies the amount of code required to render data.

Overview

Using the Mapper consists of two parts:

• Add attributes to a model class define how each property should be mapped to a data store (if at all)
• Call a method which maps properties to parameters and/or maps data results to properties

By defining metadata about the names of parameters or result columns, the Mapper can automatically map properties to columns and/or parameters. Several query methods on both Database connections and ShardSets implicitly use the Mapper.

Performance

The ArgentSea Mapper is written to be as high-performance as optimized hand-coded data access code. However, there is a hitch.

Property attributes can only be retrieved using reflection, which is relatively slow .NET code. To avoid this type of performance penalty on every data access, ArgentSea uses reflection only the first time the mapping is performed; using that metadata it then creates and compiles an “Expression Tree”to build an optimized, compiled mapping. The compiled code is cached in memory and reused for all subsequent calls.

Warning

The Mapper will be relatively slow (and CPU intensive) the first time each model class is mapped to parameters or data. The initial compilation usually takes less than a second. Subsequent calls will execute the data to property mapping at native machine-code speeds. When the application is restarted, the memory is cleared and the compilation overhead occurs again.

Missing Parameters or Columns

In some cases, the Model may have more properties than are defined in a parameter list or in data reader columns. When this happens, ArgentSea is somewhat forgiving.

As part of a Query definition (QueryStatement or QueryProcedure class), you can optionally specify the parameter set. If set, only parameters included in this list will be mapped from the Model object. This is a great way to suppress values not needed for this particular request. Of course, if the Mapper sets/reads/writes parameters and the query does not include that parameter, ADO.NET will return an error if the query is sent to the database.

If a data reader result does not contain an expected column, the property is simply ignored. If the logging level is “Debug” or lower, a log message will be created including the Model name and column name.

Next: Property Attributes