How to implement "entity joins" with filtering in Hot Chocolate

[KaTo-79]

Hi folks,

I'm pretty new to Hot Chocolate and GraphQL, so maybe this is a really obvious or easy to answer thing (or something that does not work at all). But I couldn't find anything that answered my question in the documentation or by searching the web. So I hope you guys can give me a hand...

Let's say I have a one to many relation between two entities. Let's call them "Company" and "Site". Each company can have many sites and each site belongs to exactly one company. The entities are stored in a MongoDb in collections called "companies" and "sites". The representations could for example be something like this

{
  //Company in collection "companies"
  "_id": "4711-1234",
  "name": "Example Inc."
}

{
  //Site in collection "sites"
  "_id": "8765-5678",
  "name": "Somewhere",
  "companyId": "4711-1234"
}

Now I want to be able to do GraphQL queries like this:

{
  site {
    name
    company {
      name
    }
}

or

{
  company {
    name
    sites {
      name
    }
}

and with filtering for example

{
  getSites(where: { company: { id : {eq : "4711-1234"} } }) {
    name
  }
}

or

{
  getSites(where: { company: { name : {startsWith: "Ex"} } }) {
    name
  }
}

For brevity I omit the results that I would expect. I guess that's obvious.

While I think I know how to accomplish a schema that can answer the first and second query, I have no clue how to do it in a way that the filtering would also work. Is that even possible? If yes, could you give an example (and maybe add it to the documentation)? Is there a limitation on how deep the graph can be that I want to query?

If it is not possible, could you give me a hint how to get as close as possible to what I want to achieve? Or would the only possibility be to run my own filtering implementation?

Thanks for your help...

[anilknarayan]

Something like this
`
using HotChocolate;
using HotChocolate.Data;

namespace YourNameSpace
{
public class Query
{
[UseDbContext(typeof(YourDbContext))]
[UseFiltering]
[UseProjection]
public IQueryable GetSites(
[ScopedService] YourDbContext context)
{
return context.Sites;
}
}

public partial class Company
{
    public Company()
    {
        Sites = new HashSet<Site>();
    }

    public string Name { get; set; }

[UseFiltering]
    public virtual ICollection<Site> Sites { get; set; }

}

public partial class Site
{
      public Site() {}
    
      public string Name { get; set; }
  [UseFiltering]
  public Company Company { get; set; }
}

}
`
Note the use of UseFiltering attribute in the Sites property and Company property. That is what allows you to filter by properties of a site. Also the Query class is decorated with UseFiltering and UseProjection attributes.

In the Startup.cs class you would .AddFiltering and .AddProjections as follows -
`
public void ConfigureServices(IServiceCollection services)
{
...

		services
			.AddGraphQLServer()
			...
			.AddQueryType<Query>()
			.AddProjections()
			.AddFiltering();
    }

`

[KaTo-79]

Good morning,

sorry for the late response but I had some private issues that needed my attentions. Back to topic...

I had a look at your suggestion @anilknarayan and while this is a great help for setting up the schema properly, I can't find a way to make the queries actually work. For example, if I do a query like this

{
  getSites(where: {company: {id: {eq: "<some_id>"}}}) {
    name
    shortname
  }
}

I always get an error

{
  "errors": [
    {
      "message": "Unexpected Execution Error",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "getSites"
      ],
      "extensions": {
        "message": "{document}.Company.Id is not supported.",
        "stackTrace": "<left out for readability>"
      }
    }
  ],
  "data": {
    "getSites": null
  }
}

So I guess I'm still missing something or expecting the wrong things. This is my Code as I use it right now:

//Entities
public abstract class TenantObject
{
    [Required]
    public string Id { get; set; } = default!;
}

public abstract class DeletableTenantObject : TenantObject
{
    public bool Deleted { get; set; } = false;
}

public class Company : DeletableTenantObject
{
    [Required]
    public string Name { get; set; } = default!;
    public string? Shortname { get; set; }

    public ICollection<Site> Sites { get; set; } = new List<Site>();
}

public class Site : DeletableTenantObject
{
    [Required]
    public string Name { get; set; } = default!;

    public string? Shortname { get; set; }

    [Required]
    public string CompanyId { get; set; } = default!;

    public Company? Company { get; set; }
}

//Repositories

public interface IRepository<T> where T : TenantObject
{
    IQueryable<T> GetAll();
}

public interface ICompanyRepository : IRepository<Company> { }

public interface ISiteRepository : IRepository<Site> { }

public abstract class MongoRepository<T> : IRepository<T> where T : TenantObject
{
    protected IMongoCollection<T> Collection { get; }

    protected MongoRepository(IMongoDatabase database, string collectionName)
    {
        if (database is null) throw new ArgumentNullException(nameof(database));
        if (string.IsNullOrWhiteSpace(collectionName))
            throw new ArgumentException("Collection name must not be empty", nameof(collectionName));

        Collection = database.GetCollection<T>(collectionName);
    }

    public IQueryable<T> GetAll() => Collection.AsQueryable();
}

internal sealed class CompanyRepository : MongoRepository<Company>, ICompanyRepository
{
    public CompanyRepository(IMongoDatabase database) : base(database, "companies") { }
}

internal sealed class SiteRepository : MongoRepository<Site>, ISiteRepository
{
    public SiteRepository(IMongoDatabase database) : base(database, "sites") { }
}

//BSON mapping

private static void RegisterMappings()
{
    var conventions = new ConventionPack { new LowerCaseFieldConvention() };

    ConventionRegistry.Register("TenantObject conventions", conventions, t => t.IsAssignableTo(typeof(TenantObject)));

    var tenantObjects = typeof(TenantObject).Assembly.GetTypes().Where(
        t => t.IsAssignableTo(typeof(TenantObject)) && !t.IsAbstract
    );

    var deletableTenantObjects = typeof(DeletableTenantObject).Assembly.GetTypes().Where(
        t => t.IsAssignableFrom(typeof(DeletableTenantObject)) && !t.IsAbstract
    );

    BsonClassMap.RegisterClassMap<TenantObject>(
        cm =>
        {
            foreach (var implementation in tenantObjects)
            {
                cm.AddKnownType(implementation);
            }

            cm.MapIdMember(to => to.Id).SetElementName("_id");

            cm.SetIgnoreExtraElements(true);
            cm.SetIgnoreExtraElementsIsInherited(true);
        }
    );

    BsonClassMap.RegisterClassMap<DeletableTenantObject>(
        cm =>
        {
            foreach (var implementation in deletableTenantObjects)
            {
                cm.AddKnownType(implementation);
            }

            cm.MapMember(dto => dto.Deleted).SetElementName("_deleted");
        }
    );

    BsonClassMap.RegisterClassMap<Site>(
        cm =>
        {
            cm.AutoMap();
            cm.MapMember(s => s.CompanyId).SetElementName("company");
            cm.UnmapMember(s => s.Company);
        }
    );

    BsonClassMap.RegisterClassMap<Company>(
        cm =>
        {
            cm.AutoMap();
            cm.UnmapMember(c => c.Sites);
        }
    );
}

//GraphQL types
public class CompanyGraphType : ObjectType<Company>
{
    protected override void Configure(IObjectTypeDescriptor<Company> descriptor)
    {
        descriptor
            .Field(c => c.Sites)
            .Type<ListType<SiteGraphType>>()
            .ResolveWith<CompanyResolver>(r => r.GetSites(default!, default!))
            .UseFiltering();
    }

    private class CompanyResolver
    {
        public IQueryable<Site> GetSites([Parent] Company company, [Service] ISiteRepository siteRepository) => 
            siteRepository.GetAll().Where(s => s.CompanyId == company.Id).AsQueryable();
    }
}

public class SiteGraphType : ObjectType<Site>
{
    protected override void Configure(IObjectTypeDescriptor<Site> descriptor)
    {
        descriptor.Ignore(f => f.CompanyId);

        descriptor
            .Field(s => s.Company)
            .ResolveWith<SiteResolver>(r => r.GetCompany(default!, default!))
            .UseFiltering();
    }

    private class SiteResolver
    {
        public Company GetCompany([Parent] Site site, [Service] ICompanyRepository companyRepository) =>
            companyRepository.GetAll().Single(c => c.Id == site.CompanyId);
    }
}

//GraphQL queries

public class CompanyQueries : ObjectTypeExtension
{
    protected override void Configure(IObjectTypeDescriptor descriptor)
    {
        descriptor.Name(OperationTypeNames.Query);

        descriptor.Field("getCompanies")
            .Type<ListType<CompanyGraphType>>()
            .ResolveWith<CompanyQueryResolver>(r => r.GetCompanies(default!))
            .UseFiltering();
    }

    private class CompanyQueryResolver
    {
        public IQueryable<Company> GetCompanies([Service] ICompanyRepository companyRepository) =>
            companyRepository.GetAll();
    }
}

public class SiteQueries : ObjectTypeExtension
{        
    protected override void Configure(IObjectTypeDescriptor descriptor)
    {
        descriptor.Name(OperationTypeNames.Query);

        descriptor.Field("getSites")
            .Type<ListType<SiteGraphType>>()
            .ResolveWith<SiteQueryResolver>(r => r.GetSites(default!))
            .UseFiltering();
    }

    private class SiteQueryResolver
    {
        public IQueryable<Site> GetSites([Service] ISiteRepository siteRepository) => siteRepository.GetAll();
    }
}

Any ideas?

[KaTo-79]

OK, seems like I had a wrong assumption about how filtering works in Hot Chocolate. Finally @anilknarayan gave the right hint for building the schema. That is why I will accept it as an answer. But to make it work down to the database I had to change the repositories to join in the missing data. I'm not sure if that will fit my needs. But at least I have a deeper understanding of Hot Chocolate and MongoDB now.

[Sonic198]

can you share some code?