private static Action <DbDataReader, T> GenerateAssignment <T>(INameResolver nameResolver, DbDataReader reader) where T : new()
{
var expressions = new List <Expression>();
var t = typeof(T);
var targetParam = Expression.Parameter(t);
var valueVariable = Expression.Variable(typeof(object));
var readerParam = Expression.Parameter(typeof(DbDataReader));
var getValueMethod = typeof(DbDataReader).GetTypeInfo().GetMethod("GetValue");
#if DEBUG
var exceptionConstructor = typeof(InvalidCastException).GetConstructor(new [] { typeof(string), typeof(Exception) });
var exceptParam = Expression.Parameter(typeof(Exception));
#endif
for (var i = 0; i < reader.VisibleFieldCount; i++)
{
var dbName = reader.GetName(i);
var csharpName = nameResolver.DbToCSharp(dbName);
expressions.Add(Expression.Assign(valueVariable, Expression.Call(readerParam, getValueMethod, Expression.Constant(i))));
Expression notNullBranch = null;
if (csharpName == t.Name)
{
csharpName += "F";
}
var field = t.GetTypeInfo().GetField(csharpName);
if (field != null)
{
var fi = field.FieldType.GetTypeInfo();
foreach (var tcs in TypeConversionSpecializationsWithDefault)
{
if (tcs.Matches(fi, field.FieldType))
{
#if DEBUG
notNullBranch = Expression.TryCatch(
Expression.Assign(
Expression.Field(targetParam, field),
tcs.Convert(fi, field.FieldType, valueVariable)
),
Expression.Catch(exceptParam, Expression.Throw(Expression.New(exceptionConstructor, Expression.Constant(field.Name), exceptParam), field.FieldType))
);
#else
notNullBranch = Expression.Assign(
Expression.Field(targetParam, field),
tcs.Convert(fi, field.FieldType, valueVariable)
);
#endif
break;
}
}
}
else
{
var property = t.GetTypeInfo().GetProperty(csharpName);
if (property == null)
{
throw new ArgumentException($"field or property {csharpName} on type {t} not found for database column {dbName}");
}
var ti = property.PropertyType.GetTypeInfo();
foreach (var tcs in TypeConversionSpecializationsWithDefault)
{
if (tcs.Matches(ti, property.PropertyType))
{
#if DEBUG
notNullBranch = Expression.TryCatch(
Expression.Assign(
Expression.Property(targetParam, property),
tcs.Convert(ti, property.PropertyType, valueVariable)
),
Expression.Catch(exceptParam, Expression.Throw(Expression.New(exceptionConstructor, Expression.Constant(property.Name), exceptParam), property.PropertyType))
);
#else
notNullBranch = Expression.Assign(
Expression.Property(targetParam, property),
tcs.Convert(ti, property.PropertyType, valueVariable)
);
#endif
break;
}
}
}
var dbNullTest = Expression.Equal(valueVariable, Expression.Constant(DBNull.Value));
expressions.Add(Expression.IfThen(Expression.IsFalse(dbNullTest), notNullBranch));
}
var block = Expression.Block(
new[] {
valueVariable
},
expressions.ToArray()
);
var action = Expression.Lambda <Action <DbDataReader, T> >(block, readerParam, targetParam).Compile();
return(action);
}