private static RuleExpr <T, RuleExprContext <string> > GetValueImpl <T>(string key)
{
return(context =>
{
var applicant = context.Applicants[context.Selector];
if (applicant.KeyValueMap.TryGetValue(key, out var value))
{
if (!(value is T))
{
throw new Exception($"Failed to retrieve value for key {key} for applicant {applicant.Id} due to type mismatch. Got {value.GetType().Name}, expected {typeof(T).Name}");
}
return (Option <T> .Some((T)value), context);
}
if (!applicant.Loaders.Any())
{
throw new Exception($"Failed to load value for key {key} for applicant {applicant.Id}");
}
var newContext = context with
{
Applicants = context.Applicants.SetItem(context.Selector, applicant with
{
Loaders = applicant.Loaders.Skip(1),
KeyValueMap = applicant.Loaders.First().Load(applicant.Id, key, applicant.KeyValueMap)
})
};
return GetValueImpl <T>(key)(newContext);
});
}
public static RuleExprAst <T, RuleExprContext <string> > GetValue <T>(string key)
{
return
(new RuleExprAst <T, RuleExprContext <string> >
{
Expression = context => GetValueImpl <T>(key)(context)
});
}
/// <summary>
/// Provides strongly-typed access to the value of the field
/// identified by ordinal position.
/// </summary>
/// <remarks>
/// If <typeparamref name="T"/> is a reference type and the field
/// value is <see cref="DBNull.Value"/> then the returned value is
/// a null reference. If <typeparamref name="T"/> is a value type
/// and the field value is <see cref="DBNull.Value"/> then
/// <see cref="InvalidCastException"/> is raised unless
/// <typeparamref name="T"/> is nullable (<see cref="Nullable{T}"/>).
/// </remarks>
public static T GetValue <T>(this IDataRecord record, int i)
{
if (record == null)
{
throw new ArgumentNullException("record");
}
return(GetValueImpl <T> .Impl(record[i]));
}
private static RuleExpr <IEnumerable <T>, RuleExprContext <Unit> > GetValuesImpl <T>(string key)
{
return(context =>
{
var result = new List <T>();
var scontext = context.WithSelector <string>(null);
foreach (var applicantId in context.Applicants.Keys)
{
scontext = scontext.WithSelector(applicantId);
var(maybeValue, newSContext) = GetValueImpl <T>(key)(scontext);
if (!maybeValue.IsSome(out var value))
{
throw new Exception("Internal error. GetValue should never return nothing (it should throw instead).");
}
result.Add(value);
}
return (Option <IEnumerable <T> > .Some(result), scontext.WithSelector(Unit.Value));
});
}
