/// <summary>
/// Creates an <see cref="Expression{TDelegate}"/> that
/// produces an instance of <typeparamref name="T"/> based an a <see cref="IDataRecord"/>.
/// </summary>
/// <param name="dataRecord">The <see cref="IDataRecord"/> that represents the available fields/columns.</param>
/// <returns>An <see cref="Expression{TDelegate}"/> that represents creating an instance of <typeparamref name="T"/>.</returns>
public Expression <Func <IDataRecord, T> > CreateExpression(IDataRecord dataRecord)
{
int[] ordinals = ordinalSelector.Execute(typeof(T), dataRecord);
Func <IDataRecord, int[], T> createInstanceMethod = propertyMapperDelegateBuilder.CreateMethod(typeof(T));
var ordinalsExpression = Expression.Constant(ordinals, typeof(int[]));
var createInstanceMethodExpression = Expression.Constant(createInstanceMethod, typeof(Func <IDataRecord, int[], T>));
ParameterExpression datarecordExpression = Expression.Parameter(typeof(IDataRecord), "dataRecord");
var invokeExpression = Expression.Invoke(createInstanceMethodExpression, new Expression[] { datarecordExpression, ordinalsExpression });
ParameterExpression instanceExpression = Expression.Variable(typeof(T), "instance");
BinaryExpression assignExpression = Expression.Assign(instanceExpression, invokeExpression);
Expression <Action <IDataRecord, T> > manyToOneExpression = manyToOneExpressionBuilder.CreateExpression <T>(dataRecord);
BlockExpression blockExpression;
if (manyToOneExpression != null)
{
blockExpression = Expression.Block(new[] { instanceExpression }, assignExpression, CreateInvocationExpression(manyToOneExpression, datarecordExpression, instanceExpression), instanceExpression);
}
else
{
blockExpression = Expression.Block(new[] { instanceExpression }, assignExpression);
}
var lambda = Expression.Lambda <Func <IDataRecord, T> >(blockExpression, new[] { datarecordExpression });
return(lambda);
}
/// <summary>
/// Executes the selector and returns the ordinals required to read the columns from the data record.
/// </summary>
/// <param name="type">The <see cref="Type"/> for which to return the ordinals.</param>
/// <param name="dataRecord">The <see cref="IDataRecord"/> that represents the available fields/columns.</param>
/// <returns>A list of ordinals.</returns>
public int[] Execute(Type type, IDataRecord dataRecord)
{
return(cache.GetOrAdd(type, t => ordinalSelector.Execute(t, dataRecord)));
}
