如何一次查询多个实体?

虽然我确实收到了一些及时的答复,我为此感谢大家。我收到的回复中显示的方法不起作用。

我不得不不断地寻找,直到我最终找到了一种方法来做我需要的事情 Microsoft Forums .

简而言之,它的扩展方法如下:

    public static IQueryable<T> WhereIn<T, TValue>(this IQueryable<T> source, Expression<Func<T, TValue>> propertySelector, params TValue[] values)
    {
        return source.Where(GetWhereInExpression(propertySelector, values));
    }

    public static IQueryable<T> WhereIn<T, TValue>(this IQueryable<T> source, Expression<Func<T, TValue>> propertySelector, IEnumerable<TValue> values)
    {
        return source.Where(GetWhereInExpression(propertySelector, values));
    }

    private static Expression<Func<T, bool>> GetWhereInExpression<T, TValue>(Expression<Func<T, TValue>> propertySelector, IEnumerable<TValue> values)
    {
        ParameterExpression p = propertySelector.Parameters.Single();
        if (!values.Any())
            return e => false;

        var equals = values.Select(value => (Expression)Expression.Equal(propertySelector.Body, Expression.Constant(value, typeof(TValue))));
        var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

        return Expression.Lambda<Func<T, bool>>(body, p);
    }

int[] productList = new int[] { 1, 2, 3, 4 };

var myProducts = from p in db.Products
                 where productList.Contains(p.ProductID)
                select p;

这是SQL中查询的精确表示形式。

var myProducts = from p in db.Products
                 where productList.Contains(p.ProductID)
                select p;

如果是实体,你能更好地描述问题吗?

确切的SQL表示将是。。。

SELECT [t0].[ProductID], [t0].[Name], [t0].[ProductNumber], [t0].[MakeFlag], [t0].[FinishedGoodsFlag], 
[t0].[Color], [t0].[SafetyStockLevel], [t0].[ReorderPoint], [t0].[StandardCost], [t0].[ListPrice], 
[t0].[Size], [t0].[SizeUnitMeasureCode], [t0].[WeightUnitMeasureCode], [t0].[Weight], [t0].[DaysToManufacture], 
[t0].[ProductLine], [t0].[Class], [t0].[Style], [t0].[ProductSubcategoryID], [t0].[ProductModelID], 
[t0].[SellStartDate], [t0].[SellEndDate], [t0].[DiscontinuedDate], [t0].[rowguid], [t0].[ModifiedDate]
FROM [Production].[Product] AS [t0]
WHERE [t0].[ProductID] IN (@p0, @p1, @p2, @p3)