/// <summary>
/// Generate the method body for reading a IDataReader
/// </summary>
static Expression GenerateMethodBody(Expression reader, ValueMapping mapping)
{
var br = Expression.Label("break");
var itemType = (mapping is ValueMapping typed ? typed.Type : typeof(object));
var listType = typeof(List <>).MakeGenericType(itemType);
var list = Expression.Variable(listType, "items");
var listInit = Expression.Assign(list, Expression.New(listType));
var loopCond = Expression.IfThen(
Expression.Not(Expression.Call(reader, "Read", new Type[0])),
Expression.Break(br)
);
var loop = Expression.Loop(
Expression.Block(
loopCond,
GenerateLoopBody(reader, list, mapping)
)
, br);
var body = Expression.Block(
new ParameterExpression[] { list },
new Expression[] { listInit,
loop,
list }
);
return(body);
}
/// <summary>
/// Generate an expression for a given mapping
/// </summary>
static Expression GenerateMapping(Expression reader, ValueMapping mapping)
{
switch (mapping)
{
case SingularMapping singular:
return(GenerateSingularMapping(reader, singular));
case CtorMapping ctor:
return(GenerateCtorMapping(reader, ctor));
case NullMapping _:
throw new ArgumentException($"No mapping found between data reader columns and type '{mapping.Type}'");
default:
throw new ArgumentException();
}
}
/// <summary>
/// Generate a method that takes a data reader and return a list of readed items
/// </summary>
/// <typeparam name="TReader">Specific reader type</typeparam>
/// <typeparam name="TItem">Row type</typeparam>
/// <param name="mapping">Constructor mapping</param>
public static Expression <Func <TReader, List <TItem> > > GenerateReaderMethod <TReader, TItem>(ValueMapping mapping)
{
var readerType = typeof(TReader);
if (readerType.IsInterface)
{
throw new ArgumentException("Pass an specific reader type");
}
var readerArg = Expression.Parameter(readerType, "reader");
var body = GenerateMethodBody(readerArg, mapping);
return(Expression.Lambda <Func <TReader, List <TItem> > >(body, readerArg));
}
public static Expression GenerateLoopBody(Expression reader, Expression list, ValueMapping mapping)
{
var itemType = (mapping is ValueMapping typed ? typed.Type : typeof(object));
var body = new List <Expression>();
var itemVar = Expression.Variable(itemType, "item");
body.Add(Expression.Assign(itemVar, GenerateMapping(reader, mapping)));
body.Add(Expression.Call(list, "Add", new Type[0], itemVar));
var ret = Expression.Block(
new[] { itemVar },
body.ToList()
);
return(ret);
}
