public override Maybe<QueryResult> VisitSel_item(QueryParser.Sel_itemContext context)
{
var distinct = context.sel_modifier()?.DISTINCT() != null;
var alias = context.identifier();
var dict = new Dictionary<Attribute, List<Value>>();
foreach (var son in _zmi.Sons)
{
foreach (var (k, v) in son.Attributes)
{
if (dict.TryGetValue(k, out var l))
l.Add(v);
else
dict.Add(k, new List<Value> {v});
}
}
var (attributes, values) = _table.Columns
.Where(c => !Attribute.IsQuery(c))
.Select(c => (key: c, value: _table.GetColumn(c)))
.ToList()
.Unzip(pair => pair.key, pair => pair.value);
var env = new Environment(
new TableRow(values.Select(list =>
list.IsNull || ((AttributeTypeCollection) list.AttributeType).ElementType ==
AttributeTypePrimitive.Null
? ValueNull.Instance as Value
: list)), attributes, true);
var result = new CondExprVisitor(_zmi, env).Visit(context.cond_expr());
return result.Bind(res =>
{
switch (res)
{
case ResultSingle _:
break;
default:
throw new ArgumentException("Could not return result which is not aggregated");
}
return alias == null
? new QueryResult(res.Value).Just()
: new QueryResult(new Attribute(alias.GetText()), res.Value).Just();
});
}
/// <summary>
/// Visit a parse tree produced by <see cref="QueryParser.sel_item"/>.
/// <para>
/// The default implementation returns the result of calling <see cref="AbstractParseTreeVisitor{Result}.VisitChildren(IRuleNode)"/>
/// on <paramref name="context"/>.
/// </para>
/// </summary>
/// <param name="context">The parse tree.</param>
/// <return>The visitor result.</return>
public virtual Result VisitSel_item([NotNull] QueryParser.Sel_itemContext context)
{
return(VisitChildren(context));
}
