如何使用objectify-appengine在数据库中找到最近的点 [英] How to find the closest point in the DB using objectify-appengine

问题描述

我在我的应用程序中使用了objectify-appengine。在DB中，我存储了纬度&地方的经度。
在某些时候，我想找到最接近的地方（从数据库）到特定点。

据我所知，我不能执行常规的类似SQL的查询。
所以我的问题是如何以最好的方式完成？

I'm using objectify-appengine in my app. In the DB I store latitude & longitude of places. at some point I'd like to find the closest place (from the DB) to a specific point.
As far as i understood i can't perform regular SQL-like queries. So my question is how can it be done in the best way?

推荐答案

你应该看看< href =https://developers.google.com/maps/articles/geospatial> GeoModel ，它可以使用Google App Engine启用地理空间查询。

You should take a look at GeoModel, which enables Geospatial Queries with Google App Engine.

更新：

假设您在Objectify注释模型类中有一个GeoPt属性，名为 coordinates 。

Let's assume that you have in your Objectify annotated model class, a GeoPt property called coordinates.

您需要在您的项目中拥有两个库：

You need to have in your project two libraries:

1. GeoLocation.java


2. Java GeoModel

1. GeoLocation.java
2. Java GeoModel

在您想要执行地理查询的代码中，您有以下内容：

In the code that you want to perform a geo query, you have the following:

import com.beoui.geocell.GeocellManager;
import com.beoui.geocell.model.BoundingBox;
import you.package.path.GeoLocation;
// other imports

// in your method
GeoLocation specificPointLocation = GeoLocation.fromDegrees(specificPoint.latitude, specificPoint.longitude);
GeoLocation[] bc = specificPointLocation.boundingCoordinates(radius);

// Transform this to a bounding box
BoundingBox bb = new BoundingBox((float) bc[0].getLatitudeInDegrees(),
                 (float) bc[1].getLongitudeInDegrees(),
                 (float) bc[1].getLatitudeInDegrees(),
                 (float) bc[0].getLongitudeInDegrees());

// Calculate the geocells list to be used in the queries (optimize
// list of cells that complete the given bounding box)
List<String> cells = GeocellManager.bestBboxSearchCells(bb, null);

// calculate geocells of your model class instance
List <String> modelCells = GeocellManager.generateGeoCell(myInstance.getCoordinate);

// matching
for (String c : cells) {
    if (modelCells.contains(c)) {
        // success, do sth with it
        break;
    }
}

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