Spatial Data

Experimental With version 11 we release support for spatial data. This feature is not totally finished and polished yet. Spatial types is a community-driven feature. As the core team has little experience with spatial data, we need you feedback and decided to release what we have. It is important for use to deliver you the best experience, so reach out to us if you run into issues or have ideas to improve it. We try not to introduce breaking changes, but we save ourself the possibility to make changes to the api in future releases when we find flaws in the current design.

Spatial data describes locations or shapes in form of objects. Many database providers have support for storing this type of data. APIs often use GeoJSON to send spatial data over the network.

The most common library used for spatial data in .NET is NetTopologySuite. Entity Framework supports Spatial Data and uses NetToplogySuite as its data representation.

The package HotChocolate.Spatial integrates NetTopologySuite into HotChocolate. With this package your resolvers can return NetTopologySuite shapes and they will be transformed into GeoJSON.

Getting Started

You first need to add the package reference to your project. You can do this with the dotnet cli:

Bash
dotnet add package HotChocolate.Spatial

To make the schema recognize the spatial types you need to register them on the schema builder.

C#
services
.AddGraphQLServer()
.AddSpatialTypes();

All NetToplogySuite runtime types are now bound to the corresponding GeoJSON type.

C#
public class Pub
{
public int Id { get; set; }
public string Name { get; set; }
public Point Location { get; set; }
}
public class Query
{
// we use ef in this example
[UseDbContext(typeof(SomeDbContext))]
public IQueryable<Pub> GetPubs([ScopedService] SomeDbContext someDbContext)
{
return someDbContext.Pubs;
}
}
SDL
type Pub {
id: Int!
name: String!
location: GeoJSONPointType!
}
type Query {
pubs: [Pub!]!
}
GraphQL
{
pubs {
id
location {
__typename
bbox
coordinates
crs
type
}
name
}
}
JSON
{
"data": {
"pubs": [
{
"id": 1,
"location": {
"__typename": "GeoJSONPointType",
"bbox": [12, 12, 12, 12],
"coordinates": [[12, 12]],
"crs": 4326,
"type": "Point"
},
"name": "The Winchester"
},
{
"id": 2,
"location": {
"__typename": "GeoJSONPointType",
"bbox": [43, 534, 43, 534],
"coordinates": [[43, 534]],
"crs": 4326,
"type": "Point"
},
"name": "Fountains Head"
}
]
}
}

Spatial Types

HotChocolate supports GeoJSON input and output types. There is also a GeoJSON scalar to make generic inputs possible.

Output Types

The following mappings are available by default:

NetTopologySuiteGraphQL
PointGeoJSONPointType
MultiPointGeoJSONMultiPointType
LineStringGeoJSONLineStringType
MultiLineStringGeoJSONMultiLineStringType
PolygonGeoJSONPolygonType
MultiPolygonGeoJSONMultiPolygonType
GeometryGeoJSONInterface

All GeoJSON output types implement the following interface.

SDL
interface GeoJSONInterface {
"The geometry type of the GeoJson object"
type: GeoJSONGeometryType!
"The minimum bounding box around the geometry object"
bbox: [Float]
"The coordinate reference system integer identifier"
crs: Int
}

A NetTopologySuite.Gemeotry is mapped to this interface by default.

Input Types

For each output type there is a corresponding input type

NetTopologySuiteGraphQL
PointGeoJSONPointInput
MultiPointGeoJSONMultiPointInput
LineStringGeoJSONLineStringInput
MultiLineStringGeoJSONMultiLineStringInput
PolygonGeoJSONPolygonInput
MultiPolygonGeoJSONMultiPolygonInput

Scalar

With interfaces or unions it is possible to have multiple possible return types. Input types do not yet have a way of defining multiple possibilities. As an addition to output and input types there is the Geometry scalar, which closes this gap. When a resolver expects any Geometry type as an input, you can use this scalar. This scalar should be used with caution. Input and output types are much more expressive than a custom scalar.

SDL
scalar Geometry

Projections

To project spatial types, a special handler is needed. This handler can be registered on the schema with .AddSpatialProjections()

C#
services
.AddGraphQLServer()
.AddProjections()
.AddSpatialTypes()
.AddSpatialProjections()

The projection middleware will use this handler to project the spatial data directly to the database

C#
[UseDbContext(typeof(SomeDbContext))]
[UseProjection]
public IQueryable<Pub> GetPubs([ScopedService] SomeDbContext someDbContext)
{
return someDbContext.Pubs;
}
GraphQL
{
pubs {
id
location {
__typename
bbox
coordinates
crs
type
}
name
}
}
SQL
SELECT p."Id", p."Location", p."Name"
FROM "Pubs" AS p

Filtering

Entity framework supports filtering on NetTopologySuite objects. HotChocolate.Spatial provides handlers for filtering spatial types on IQueryable. These handlers can be registered on the schema with .AddSpatialFiltering()

C#
services
.AddGraphQLServer()
.AddProjections()
.AddSpatialTypes()
.AddSpatialFiltering()

After the registration of the handlers UseFiltering() will infer the possible filter types for all Geometry based types.

C#
[UseDbContext(typeof(SomeDbContext))]
[UseFiltering]
public IQueryable<Pub> GetPubs([ScopedService] SomeDbContext someDbContext)
{
return someDbContext.Pubs;
}
SDL
type Query {
pubs(where: PubFilterInput): [Pub!]!
}
input PubFilterInput {
and: [PubFilterInput!]
or: [PubFilterInput!]
id: ComparableInt32OperationFilterInput
name: StringOperationFilterInput
location: PointFilterInput
}
input PointFilterInput {
and: [PointFilterInput!]
or: [PointFilterInput!]
m: ComparableDoubleOperationFilterInput
x: ComparableDoubleOperationFilterInput
y: ComparableDoubleOperationFilterInput
z: ComparableDoubleOperationFilterInput
area: ComparableDoubleOperationFilterInput
boundary: GeometryFilterInput
centroid: PointFilterInput
dimension: DimensionOperationFilterInput
envelope: GeometryFilterInput
geometryType: StringOperationFilterInput
interiorPoint: PointFilterInput
isSimple: BooleanOperationFilterInput
isValid: BooleanOperationFilterInput
length: ComparableDoubleOperationFilterInput
numPoints: ComparableInt32OperationFilterInput
ogcGeometryType: OgcGeometryTypeOperationFilterInput
pointOnSurface: PointFilterInput
srid: ComparableInt32OperationFilterInput
contains: GeometryContainsOperationFilterInput
distance: GeometryDistanceOperationFilterInput
intersects: GeometryIntersectsOperationFilterInput
overlaps: GeometryOverlapsOperationFilterInput
touches: GeometryTouchesOperationFilterInput
within: GeometryWithinOperationFilterInput
ncontains: GeometryContainsOperationFilterInput
ndistance: GeometryDistanceOperationFilterInput
nintersects: GeometryIntersectsOperationFilterInput
noverlaps: GeometryOverlapsOperationFilterInput
ntouches: GeometryTouchesOperationFilterInput
nwithin: GeometryWithinOperationFilterInput
}

Distance

The distance filter is an implementation of Geometry.Within

The filter requires an input geometry. You can optionally buffer this geometry with the input field buffer. The filter also has all comparable filters.

SDL
input GeometryDistanceOperationFilterInput {
geometry: Geometry!
buffer: Float
eq: Float
neq: Float
in: [Float!]
nin: [Float!]
gt: Float
ngt: Float
gte: Float
ngte: Float
lt: Float
nlt: Float
lte: Float
nlte: Float
}
GraphQL
{
pubs(
where: {
location: {
within: { geometry: { type: Point, coordinates: [1, 1] }, lt: 120 }
}
}
) {
id
name
location
}
}
SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE ST_Within(c."Area", @__p_0)

The negation of this operation is nwithin

SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE NOT ST_Within(c."Area", @__p_0)

Contains

The contains filter is an implementation of Geometry.Contains

The filter requires an input geometry. You can optionally buffer this geometry with the input field buffer.

SDL
input GeometryContainsOperationFilterInput {
geometry: Geometry!
buffer: Float
}
GraphQL
{
counties(
where: {
area: { contains: { geometry: { type: Point, coordinates: [1, 1] } } }
}
) {
id
name
area
}
}
SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE ST_Contains(c."Area", @__p_0)

The negation of this operation is ncontains

SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE NOT ST_Contains(c."Area", @__p_0)

Touches

The touches filter is an implementation of Geometry.Touches

The filter requires an input geometry. You can optionally buffer this geometry with the input field buffer.

SDL
input GeometryTouchesOperationFilterInput {
geometry: Geometry!
buffer: Float
}
GraphQL
{
counties(
where: {
area: {
touches: {
geometry: {
type: Polygon,
coordinates: [[1, 1], ....]
}
}
}
}){
id
name
area
}
}
SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE ST_Touches(c."Area", @__p_0)

The negation of this operation is ntouches

SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE NOT ST_Touches(c."Area", @__p_0)

Intersects

The intersects filter is an implementation of Geometry.Intersects

The filter requires an input geometry. You can optionally buffer this geometry with the input field buffer.

SDL
input GeometryIntersectsOperationFilterInput {
geometry: Geometry!
buffer: Float
}
GraphQL
{
roads(
where: {
road: {
intersects: {
geometry: {
type: LineString,
coordinates: [[1, 1], ....]
}
}
}
}){
id
name
road
}
}
SQL
SELECT r."Id", r."Name", r."Road"
FROM "Roads" AS r
WHERE ST_Intersects(r."Road", @__p_0)

The negation of this operation is nintersects

SQL
SELECT r."Id", r."Name", r."Road"
FROM "Roads" AS r
WHERE NOT ST_Intersects(r."Road", @__p_0)

Overlaps

The overlaps filter is an implementation of Geometry.Overlaps

SDL
input GeometryOverlapsOperationFilterInput {
geometry: Geometry!
buffer: Float
}
GraphQL
{
county(
where: {
area: {
overlaps: {
geometry: {
type: Polygon,
coordinates: [[1, 1], ....]
}
}
}
}){
id
name
area
}
}
SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE ST_Overlaps(c."Area", @__p_0)

The negation of this operation is noverlaps

SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE NOT ST_Overlaps(c."Area", @__p_0)

Within

The within filter is an implementation of Geometry.Within

SDL
input GeometryWithinOperationFilterInput {
geometry: Geometry!
buffer: Float
}
GraphQL
{
pubs(
where: {
location: {
within: { geometry: { type: Point, coordinates: [1, 1] }, buffer: 200 }
}
}
) {
id
name
location
}
}
SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE ST_Within(c."Area", @__p_0)

The negation of this operation is nwithin

SQL
SELECT c."Id", c."Name", c."Area"
FROM "Counties" AS c
WHERE NOT ST_Within(c."Area", @__p_0)

What's next?

In upcoming releases spatial data will get reprojection features and sorting capabilities.

Reprojection

At the moment the coordinate reference system (crs) is fixed. The user has to know the crs of the backend to do spatial filtering. The API will furthermore always return the data in the crs it was stored in the database.

We want to improve this. The user should be able to send data to the backend without knowing what the crs. The backend should reproject the incoming data automatically to the correct crs.

Additionally we want to provide a way for users, to specify in what CRS they want to receive the data.

Sorting

Currently we only support filtering for spatial data. We also want to provide a way for users to sort results. This can e.g. be used to find the nearest result for a given point.