Question

可能重复：
Soft Delete Entity Framework Code First

在返回结果之前，有没有办法过滤实体的结果？所以说First或Find或者我选择用于对抗实体的任何方法都不会返回超过3个月的任何东西。此外，如果我包含实体，它也将被过滤。我试图使用它来实现软删除等

我希望这可以在某种程度上在内部完成，如果可能的话我可以说_db.SmallGroups.ToList()并且它会知道哪些记录没有带回来（即旧记录，IsDeleted ==真实记录）我不想必要时，必须将此逻辑放在每个查询点

先谢谢

Answer 1

当然，您可以在 where 子句

中指定条件

DateTime threeMonthsAgo = DateTime.Now.AddMonths(-3);

var results = 
    (from t in context.MyTable where t.TheTime > threeMonthsAgo select t).First();

<强>更新

根据您的评论...

您确实可以构建一个表达式，您可以将其重用为 where 条件。

这是我写的一个扩展方法，用于包含类型的条件（XML注释中引用的原始源）

/// <summary>
/// Extension method that enables .Contains(obj) like functionality for Linq to Entities.
/// 
/// Source: http://www.velocityreviews.com/forums/t645784-linq-where-clause.html
/// </summary>
/// <typeparam name="TElement">The element being evaluated by the Where clause</typeparam>
/// <typeparam name="TValue">The value to match</typeparam>
/// <param name="valueSelector">Lamda for selecting matching values</param>
/// <param name="values">IEnumerable of the values</param>
/// <returns>Expression consumable by Linq to Entities that reflects semantics of .Contains(value)</returns>
/// <remarks>
/// Usage:
/// 
/// Replace expression like 
/// 
/// where ChildrenIDs.Contains(items.CategoryID)
/// 
/// with
/// 
/// .Where((BuildContainsExpression<Item, int>(item => item.CategoryID, ChildrenIDs))
/// 
/// NOTE: If the item collection is large, the SQL query will be as well.
/// </remarks>
static public Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)
{
    if (null == valueSelector)
    {
        throw new ArgumentNullException("valueSelector");
    }
    if (null == values) { throw new ArgumentNullException("values"); }

    ParameterExpression p = valueSelector.Parameters.Single();
    if (!values.Any())
    {
        return e => false;
    }

    var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));
    var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));
    return Expression.Lambda<Func<TElement, bool>>(body, p);
}

<强>用法

HashSet<long> productCodes = new HashSet<long>(); // Populate with some product codes to match

productCodeWhere = LinqToEntitiesUtil.BuildContainsExpression<Verbatim, long>(v => v.ProductCode, productCodes);

var matching = (from v in ctx.MyTable where MY_CONDITIONS select v)
    .Where(productCodeWhere);

实体框架代码第一次过滤检索结果

1 个答案: