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问EF核心动态包含和排序
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Stack Overflow用户

提问于 2021-01-12 04:06:08

回答 1查看 248关注 0票数 0

我正在尝试包含相关实体，并对它们进行排序。

如果您知道实体和相关项，它可以像下面这样简单：

context.Set<Item>().Include(x => x.SubItems.OrderBy(x => x.Name));

现在我尝试动态地复制上面的场景，结果应该是这样的：

{[Microsoft.EntityFrameworkCore.Query.QueryRootExpression].Include(x => x.SubItems.OrderBy(y => y.Name))}

但我得到的最接近的结果是：

{[Microsoft.EntityFrameworkCore.Query.QueryRootExpression].Include(x => x.SubItems).OrderBy(y => y.Name)}

我在这里做错了什么？下面是我的代码：

    private static IQueryable<T> IncludeNaviagations<T>(DbContext context, IQueryable<T> queryable)
    {
        var type = typeof(T);

        foreach (var nav in context.Model.FindEntityType(typeof(T)).GetNavigations())
        {                
            var method = IncludeMethodInfo.MakeGenericMethod(new[] { type, type.GetProperty(nav.Name).PropertyType });

            var includeParam = Expression.Parameter(type, "x");
            var includeProperty = Expression.Property(includeParam, nav.Name);
            var includeLambda =  Expression.Lambda(includeProperty, includeParam);

            var include = Expression.Call(instance: null, method: IncludeMethodInfo.MakeGenericMethod(type, nav.PropertyInfo.PropertyType), arguments: new[] { queryable.Expression, Expression.Quote(includeLambda) });

            var orderColumn = "Name";

            var property = type.GetProperty(orderColumn);
            var param = Expression.Parameter(type, "y");
            var propName = Expression.Property(param, orderColumn);
            var sort = Expression.Lambda(propName, param);

            var result = Expression.Call(typeof(Queryable), "OrderBy", new[] { type, sort.ReturnType }, include, Expression.Quote(sort));

            queryable = queryable.Provider.CreateQuery<T>(result);
        }

        return queryable;
    }

PS。上面的方法将进行一点调整，以递归地执行includes。

entity-framework-core

ef-core-5.0

回答 1

Stack Overflow用户

回答已采纳

发布于 2021-01-14 23:49:00

在花了相当多的时间之后，我让它工作了，下面是一个拼凑起来的解决方案：

OrderByMethodInfo = typeof(Enumerable).GetMethods().First(x => x.Name == "OrderBy" && x.GetParameters().Length == 2);
    
var orderColumnType = subType.GetProperty(orderColumn).PropertyType;

orderByMethod = orderByMethod.MakeGenericMethod(subType, orderColumnType);

var includeParam = Expression.Parameter(nav.ParentType, "x");
var includeProperty = Expression.Property(includeParam, nav.Name);

var property = nav.ParentType.GetProperty(orderColumn);
var param = Expression.Parameter(subType, "y");
var propName = Expression.Property(param, orderColumn);
var sort = Expression.Lambda(propName, param);

var order = Expression.Call(orderByMethod, includeProperty, sort);
var orderLambda = Expression.Lambda(order, Expression.Parameter(nav.ParentType, "x"));
var orderQuote = Expression.Quote(orderLambda);

var includeMethod = IncludeMethodInfo.MakeGenericMethod(nav.ParentType, typeof(IOrderedEnumerable<>).MakeGenericType(subType));

result = Expression.Call(instance: null, method: includeMethod, arguments: new[] { queryable.Expression, orderQuote });

queryable.Provider.CreateQuery<object>(result);

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/65673779

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