C# LINQ to实体无法识别该方法，并且无法将该方法转换为存储表达式

这是我写的LINQtoEntities语句

public static List<Model.User> GetNearestUsers(int userid,int count,ref Model.HangoutDBEntities context)
    {
        Model.Location myLocation=GetCurrentLocation(userid,ref context);

        return context.Locations.Where(o => EntityFunctions.DiffMinutes(DateTime.Now, o.DateTimeStamp) <= 30).OrderBy(o => Core.Location.Distance.CalculateDistance(myLocation.Latitude, myLocation.Longitude, o.Latitude, o.Longitude)).Select(o => o.User).ToList();
    }

请让我知道是否有任何解决办法。我有个例外

LINQ to实体无法识别方法“Double” 计算状态（System.Decimal，System.Decimal，System.Decimal， 方法，而此方法无法转换为 存储表达式

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我知道自定义函数不适用于Linq 2实体，但我不知道如何解决这个问题。你能帮帮我吗

将数据加载到列表中，然后对列表执行计算

    var origList = context.Locations.Where(o => EntityFunctions.DiffMinutes(DateTime.Now, o.DateTimeStamp) <= 30).ToList()

 var orderedList = origList.OrderBy(o => Core.Location.Distance.CalculateDistance(myLocation.Latitude, myLocation.Longitude, o.Latitude, o.Longitude)).Select(o => o.User).ToList();

var origList=context.Locations.Where（o=>EntityFunctions.DiffMinutes（DateTime.Now，o.DateTimeStamp）Core.Location.Distance.calculateInstance（myLocation.Latitude，myLocation.Longitude，o.Latitude，o.Longitude），选择（o=>o.User.ToList（）；

或

context.Locations
.Where（o=>EntityFunctions.DiffMinutes（DateTime.Now，o.DateTimeStamp）Core.Location.Distance.calculateInstance（myLocation.Latitude，myLocation.Longitude，o.Latitude，o.Longitude））
.Select（o=>o.User）.ToList（）；

需要注意的是where子句后面的ToList

在调用ToList（）时，数据被加载到内存中，排序成为Linq对对象的一项任务

您可以定义一个自定义方法…，并告诉实体框架如何将该方法转换为SQL

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我最近不得不解决这个问题。诀窍是对大多数语句（Math.Pow除外）使用System.Data.Entity.SqlServer中的SqlFunctions，而不是System.Math

备用LINQ样式（from/where/let/orderby等）非常有用，因为let关键字允许您分解问题并保持可读性

var closestLocation = await (
    from q in qryable
    where q.LAT.HasValue && q.LONG.HasValue
    // Convert derees to radians (pi / 180 = 0.01745...)
    let dbLatitudeRadians = q.LAT.Value * 0.0174532925199433
    let dbLongitudeRadians = q.LONG.Value * 0.0174532925199433
    let requestLatitudeRadians = requestLatitude * 0.0174532925199433
    let requestLongitudeRadians = requestLongitude * 0.0174532925199433
    let deltaLatitudeRadians = requestLatitudeRadians - dbLatitudeRadians
    let deltaLongitudeRadians = requestLongitudeRadians - dbLongitudeRadians
    let sinHalfLatitudeDistance = SqlFunctions.Sin(deltaLatitudeRadians / 2) ?? 0.0
    let sinHalfLongitudeDistance = SqlFunctions.Sin(deltaLongitudeRadians / 2) ?? 0.0
    let cosThisLatitude = SqlFunctions.Cos(dbLatitudeRadians) ?? 0.0
    let cosThatLatitude = SqlFunctions.Cos(requestLatitudeRadians) ?? 0.0
    let expr = Math.Pow(sinHalfLatitudeDistance, 2) + cosThisLatitude * cosThatLatitude * Math.Pow(sinHalfLongitudeDistance, 2)
    let sqrtExpr = Math.Pow(expr, 0.5)
    let sqrt1MinusExpr = Math.Pow(1 - expr, 0.5)
    let distanceInMeters = 6376500 * 2 * SqlFunctions.Atan2(sqrtExpr, sqrt1MinusExpr)
    orderby distanceInMeters
    select q
).FirstOrDefaultAsync(cancellationToken).ConfigureAwait(false);

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如果您使用的是sql server，我强烈建议您使用空间数据类型，而不是在内存中进行计算。问题是您的计算无法转换为SQL。

context.Locations
    .Where(o => EntityFunctions.DiffMinutes(DateTime.Now, o.DateTimeStamp) <= 30).ToList()
        .OrderBy(o => Core.Location.Distance.CalculateDistance(myLocation.Latitude, myLocation.Longitude, o.Latitude, o.Longitude))
            .Select(o => o.User).ToList();

var closestLocation = await (
    from q in qryable
    where q.LAT.HasValue && q.LONG.HasValue
    // Convert derees to radians (pi / 180 = 0.01745...)
    let dbLatitudeRadians = q.LAT.Value * 0.0174532925199433
    let dbLongitudeRadians = q.LONG.Value * 0.0174532925199433
    let requestLatitudeRadians = requestLatitude * 0.0174532925199433
    let requestLongitudeRadians = requestLongitude * 0.0174532925199433
    let deltaLatitudeRadians = requestLatitudeRadians - dbLatitudeRadians
    let deltaLongitudeRadians = requestLongitudeRadians - dbLongitudeRadians
    let sinHalfLatitudeDistance = SqlFunctions.Sin(deltaLatitudeRadians / 2) ?? 0.0
    let sinHalfLongitudeDistance = SqlFunctions.Sin(deltaLongitudeRadians / 2) ?? 0.0
    let cosThisLatitude = SqlFunctions.Cos(dbLatitudeRadians) ?? 0.0
    let cosThatLatitude = SqlFunctions.Cos(requestLatitudeRadians) ?? 0.0
    let expr = Math.Pow(sinHalfLatitudeDistance, 2) + cosThisLatitude * cosThatLatitude * Math.Pow(sinHalfLongitudeDistance, 2)
    let sqrtExpr = Math.Pow(expr, 0.5)
    let sqrt1MinusExpr = Math.Pow(1 - expr, 0.5)
    let distanceInMeters = 6376500 * 2 * SqlFunctions.Atan2(sqrtExpr, sqrt1MinusExpr)
    orderby distanceInMeters
    select q
).FirstOrDefaultAsync(cancellationToken).ConfigureAwait(false);