C# MongoDB API存储GeoJSON Geometry至类的问题求助

Hey there! Let's tackle your two MongoDB API problems head-on—since your Restaurant class is working smoothly, we can use that as a reference to fix the Neighborhood class hiccups.

1. Fixing Polygon Coordinate Storage in the Neighborhood Class #

The most common issues here are mismatched field types or missing geospatial indexing. Here's what to check:

• Use the Correct GeoJSON Type: Don't store polygons as plain lists of coordinates. Instead, use your MongoDB driver's built-in GeoJSON polygon type (like GeoJsonPolygon in Java/.NET, or mongoose.Schema.Types.Polygon in Mongoose). This ensures MongoDB recognizes the data as a valid geospatial object.
  Example Java class snippet:

  public class Neighborhood {
      private String neighborhoodName;
      // Add the 2dsphere index annotation to enable geospatial queries
      @GeoSpatialIndexed(type = GeoSpatialIndexType.GEO_2DSPHERE)
      private GeoJsonPolygon boundary;
  
      // Constructor, getters, setters
  }
  

• Properly Construct the Polygon: When creating a polygon, make sure the coordinate list is closed (the first and last points must be identical) and follows MongoDB's [longitude, latitude] order (this is a super common mix-up!).
  Example of building a valid polygon:

  // Create a closed list of points (long, lat)
  List<GeoJsonPoint> polygonPoints = Arrays.asList(
      new GeoJsonPoint(-73.9857, 40.7484),
      new GeoJsonPoint(-73.9855, 40.7482),
      new GeoJsonPoint(-73.9850, 40.7486),
      new GeoJsonPoint(-73.9857, 40.7484) // Close the polygon
  );
  GeoJsonPolygon neighborhoodBoundary = new GeoJsonPolygon(Arrays.asList(polygonPoints));
  Neighborhood myNeighborhood = new Neighborhood("Upper East Side", neighborhoodBoundary);
  // Save to MongoDB
  mongoTemplate.save(myNeighborhood);
  

• Verify Index Creation: If you're not using driver annotations, manually create the 2dsphere index in the shell:

  db.neighborhoods.createIndex({ boundary: "2dsphere" })
  

2. Getting the GeoWithin Function to Work #

GeoWithin relies on proper indexing and correct query formatting. Let's fix this:

• Ensure the 2dsphere Index Exists: Without this index, geospatial queries like GeoWithin will fail. Double-check the index exists using db.neighborhoods.getIndexes() in the shell.
• Build a Valid GeoWithin Query: Use the driver's query builders to construct the query with a valid GeoJSON polygon. Here's a Java example:

  // Define the area you want to query (a polygon)
  GeoJsonPolygon queryArea = new GeoJsonPolygon(Arrays.asList(
      new GeoJsonPoint(-74.01, 40.70),
      new GeoJsonPoint(-73.99, 40.70),
      new GeoJsonPoint(-73.99, 40.72),
      new GeoJsonPoint(-74.01, 40.72),
      new GeoJsonPoint(-74.01, 40.70) // Close the query polygon
  ));
  // Create the query using GeoWithin
  Query query = new Query(Criteria.where("boundary").within(queryArea));
  List<Neighborhood> results = mongoTemplate.find(query, Neighborhood.class);
  

• Check Coordinate Order: Again, make sure you're using [longitude, latitude] in both the stored polygon and the query polygon. Swapping these will return incorrect results or no matches at all.
• Test in the Shell First: If your code query isn't working, test the equivalent shell command to rule out driver-specific issues:

  db.neighborhoods.find({
    boundary: {
      $geoWithin: {
        $geometry: {
          type: "Polygon",
          coordinates: [
            [ [-74.01, 40.70], [-73.99, 40.70], [-73.99, 40.72], [-74.01, 40.72], [-74.01, 40.70] ]
          ]
        }
      }
    }
  })
  

Quick Additional Checks #

• Compare with Restaurant Class: Since your Restaurant class works, look for differences in how you're defining fields, adding indexes, or saving data. The discrepancy is likely there.
• Check MongoDB Logs: If you're still stuck, check MongoDB's log files for error messages related to geospatial storage or queries—they'll often point you directly to the issue.
• Validate Documents with Compass: Use MongoDB Compass to inspect the Neighborhood collection. Ensure the boundary field is stored as a Polygon type (not a plain array) with valid GeoJSON structure.

内容的提问来源于stack exchange，提问作者Cannass