public IQueryable <T> Entities <T>()
{
var provider = new MyQueryProvider(this);
var query = new MyQueryable <T>(provider, this);
return(query);
}
private void CrearIQueryProperty(object obj, PropertyInfo p)
{
var provider = new MyQueryProvider(this);
Join MyAttribute = (Join)Attribute.GetCustomAttributes(p, false).FirstOrDefault(t => t is Join);
if (MyAttribute == null)
{
return;
}
PropertyInfo pJoin1 = obj.GetType().GetProperties().FirstOrDefault(t => t.GetCustomAttributes(typeof(Column), true).Length > 0 && ((Column)t.GetCustomAttributes(typeof(Column), true)[0]).Name == MyAttribute.Key);
if (pJoin1 == null)
{
pJoin1 = obj.GetType().GetProperty(MyAttribute.Key);
}
object pJoinValue1 = pJoin1.GetValue(obj, null);
Func <object, bool> g;
var tipoBase = p.PropertyType.GetGenericArguments()[0];
var delegado = typeof(Func <,>).MakeGenericType(tipoBase, typeof(bool));
var delegadoExpresion = typeof(Expression <>).MakeGenericType(delegado);
var param = Expression.Parameter(tipoBase, "e");
var predicate = LambdaExpression.Lambda(delegado, Expression.Equal(Expression.Property(param, MyAttribute.ForeignKey),
Expression.Constant(pJoinValue1)),
new ParameterExpression[] { param });
Type _tipo = typeof(MyQueryable <>).MakeGenericType(tipoBase);
var query = (IQueryable)Activator.CreateInstance(_tipo, provider, this);
query = query.Provider.CreateQuery(
Expression.Call(
typeof(Queryable), "Where",
new Type[] { tipoBase },
query.Expression, Expression.Quote(predicate)));
p.SetValue(obj, query, null);
}
private static void UseMyQueryProvider()
{
var q1 = MyQueryProvider.CreateQueryable <int>();
Console.WriteLine($"q1: {q1.Expression}");
var q2 = q1.Where(x => x % 2 == 0);
Console.WriteLine($"q2: {q2.Expression}");
var q3 = q2.Select(x => x * x);
Console.WriteLine($"q3: {q3.Expression}");
// Executeメソッドがnullのみを返すのでこのforeachで"ランタイム"エラーとなる。
// foreachのコメントアウトを外してもコンパイルは通る。
//foreach (var val in q3)
//{
// Console.WriteLine($"{val}");
//}
}
public MyQuery(IQueryable <T> queryable)
{
_queryable = queryable;
Provider = new MyQueryProvider(_queryable.Provider);
}