Question

我正在尝试编写LINQ查询，其中我要根据前端发回的内容访问两个不同表中的数据如果FlowerClients是从前端发送的，我想使用FlowerClient表，或者如果要发送的数据是用于AnotherClient的，请使用AnotherClient。

这是否可以在LINQ中进行，还是创建不同的方法更好？

var flowerById = (from flower in flowerContext.Flowers
        where flower.FlowerId == flowerId
        join petals in flowerContext.Petals on flower.PetalId equals petals.PetalId
        from flowerClients in flowerContext.FlowerClients.Where(x => x.FlowerId == flower.FlowerId).DefaultIfEmpty()
        ||
        from anotherFlowerClients in flowerContext.AnotherClients.Where(x => x.FlowerId == flower.FlowerId).DefaultIfEmpty()

Answer 1

您可能想要创建不同的方法，尤其是在FlowerClients和AnotherClients类非常不同的情况下。

否则，您可以动态生成查询表达式。您可能要确保FlowerClients和AnotherClients实现一个公共接口，但是那样就不必在两者之间进行任何映射。

IQueryable<FlowerPetal> query1 = flowerContext.Flowers
    .Where(f => f.FlowerId == flowerId)
    .Join(flowerContext.Petals,
        f => f.PetalId,
        p => p.PetalId,
        (f, p) => new FlowerPetal { Flower = f, Petal = p }
    );

IQueryable<FlowerPetalClient> WithClients(IQueryable<FlowerPetal> _query, IQueryable<IClient> _clients) =>
    _query.SelectMany(
        x => _clients.Where(c => c.FlowerId == x.Flower.FlowerId).DefaultIfEmpty(),
        (x, c) => new FlowerPetalClient { Flower = x.Flower, Petal = x.Petal, Client = c }
    );

IQueryable<IClient> clients = useFlowerClients // decide on which client to use
    ? flowerContext.FlowerClients
    : flowerContext.AnotherClients;
var query = WithClients(query1, clients); // expand on query

带有一些帮助程序类：

class FlowerPetal
{
    public Flower Flower { get; set; }
    public Petal Petal { get; set; }
}
class FlowerPetalClient
{
    public Flower Flower { get; set; }
    public Petal Petal { get; set; }
    public IClient Client { get; set; }
}

如何从语句在LINQ中执行OR

1 个答案: