Question

在Web API 2项目中，我有一个从数据库中返回项目的控制器，如此;

<Stop>
    <Connection>

LineShortName: <LineShortName>10</LineShortName>  Destination: <Destination>HAUPTBAHNHOF</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T10:52:00</ScheduledDepartureTime>  

</Connection>
    <Connection>

LineShortName: <LineShortName>2/12</LineShortName>  Destination: <Destination>WALLERSHEIM</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T10:47:00</ScheduledDepartureTime>  

</Connection>
        <Connection>

LineShortName: <LineShortName>1</LineShortName>  Destination: <Destination>GOLDGRUBE</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:16:00</ScheduledDepartureTime>  

</Connection>
    <Connection>

LineShortName: <LineShortName>1</LineShortName>  Destination: <Destination>ALTSTADT</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T10:44:00</ScheduledDepartureTime>  

</Connection>
    <Connection>

LineShortName: <LineShortName>9</LineShortName>  Destination: <Destination>KO-ZENTRUM</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:24:00</ScheduledDepartureTime>  

</Connection>

    <Connection>

LineShortName: <LineShortName>8</LineShortName>  Destination: <Destination>HAUPTBAHNHOF</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:25:00</ScheduledDepartureTime>  

</Connection>
    <Connection>

LineShortName: <LineShortName>3/13</LineShortName>  Destination: <Destination>HAUPTBAHNHOF</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:08:00</ScheduledDepartureTime>  

</Connection>

    <Connection>

LineShortName: <LineShortName>20</LineShortName>  Destination: <Destination>HAUPTBAHNHOF</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:24:00</ScheduledDepartureTime>  

</Connection>
    <Connection>

LineShortName: <LineShortName>2/12</LineShortName>  Destination: <Destination>NEUENDORF</Destination>  ScheduledDepartureTime: <ScheduledDepartureTime>2017-11-07T11:32:00</ScheduledDepartureTime>  

</Connection>

</Stop>

这可以按预期工作。

但是正如你可能猜到的那样，otherCollection可以包含与当前项目相关的x行。目前我只获得FirstOrDefault。 cX和cY是Lat和Lng坐标。

我现在需要从otherCollection中收集与当前项相关的所有坐标，并将它们作为LatLng的组合列表返回，然后我可以在函数中使用它来查找中心点（此函数I有）。

所以我想做这样的事情：

[EnableQuery()]
public IQueryable<MyList> GetList()
{
    var items = from i in db.Items
        select new ItemsList()
        {
            Id = i.Id,
            Title = i.Title,
            cX = i.otherCollection.FirstOrDefault().cX,
            cY = i.otherCollection.FirstOrDefault().cY
        };
    return items.AsQueryable();
}

var items = from i in db.Items select new ItemsList() { Id = i.Id, Title = i.Title, LatLng = GetCentralGeoCoordinate(i.otherCollection.cX.ToList() + i.otherCollection.cY.ToList()) //IList<GeoCoordinate> geoCoordinates }; return items.AsQueryable();和i.otherCollection.cX都是字符串值。

我怎么能这样做？

Answer 1

您将无法使用GetCentralGeoCoordinate作为IQueryable。如果要调用此函数，首先应将数据提取到本地内存，然后为获取序列的每个元素调用此函数。

var result = db.Items
    .Select(item => new ItemsList()
    {
        Id = item.Id,
        ...
    })
    .AsEnumerable()       // bring your items to local memory
    .Select(item => GetCentralGeoCoordinate(...);

现在每个GeoCoordinate都有两个属性：cX和cY。找到中心坐标时，您需要知道哪个cx属于哪个cy。你想要这样的东西：

var coordinates = (4, 10) (8, 15) (3, 7) ...

而不是

var xCoordintate = 4, 8, 3, ...
var yCoordinates = 10, 15, 7, ...

您的查询将是：

var items = db.Items
select (item => new ItemsList()
{
    Id = item.Id,
    Title = item.Title,
    Coordinates = item.OtherCollection
        .Select(otherCollectionItem => new Coordinate()
        {
            Cx = otherCollectionItem.Cx,
            Cy = otherCollectionItem.Cy,
        })
        .ToList(),
}
.AsEnumerable()
.Select(fetchedItem => GetCentralGeoCoordinate(fetchedItem.Coordinate));

Coordinate类是一个带有cX和cY的简单类。与System.Drawing.Point

类似

计算中心坐标的函数将采用一系列坐标并返回唯一的中心坐标（如果没有中心坐标，则可能为null）

Coordinate GetCentralGeoCoordinate(IEnumerable<Coordinate> coordinates)
{
    foreach (Coordinate coordinate in Coordinates)
    {
        ... // do something with the coordinate
    }
}

将字符串组合到Queryable中的List

1 个答案: