static Delegate CreatePrimativeMapFunc(Type typeT, IReadOnlyCollection <Column> columns)
{
Contract.Requires(typeT != null);
Contract.Requires(columns != null);
Contract.Requires(columns.Count > 0);
var col0 = columns.First();
if (!Types.AreCompatible(col0.Type, typeT))
{
Mapping._trace.OnNext($"Cannot map column {col0.Name} to {typeT} as column type {col0.Type} is not compatible");
}
var readerParam = Expression.Parameter(typeof(DbDataReader), "reader");
var resultParam = Expression.Parameter(typeT, "result");
bool readAsObject;
var getMethod = DataReaderGetMethod(col0.Type, out readAsObject);
Expression value = Expression.Call(readerParam, getMethod, Expression.Constant(0));
if (readAsObject)
{
value = Expression.Convert(value, col0.Type);
}
if (col0.Type != typeT)
{
value = ConvertOrCastValue(value, col0.Type, typeT);
}
var body = Expression.Condition(
Expression.IsTrue(Expression.Call(readerParam, typeof(DbDataReader).GetMethod("IsDBNull", new[] { typeof(int) }), Expression.Constant(0))),
Expression.Default(typeT),
value);
var func = typeof(Func <,>).MakeGenericType(new[] { typeof(DbDataReader), typeT });
return(Expression.Lambda(func, body, new[] { readerParam }).Compile());
}
