GraphQL queries with tables join using Node.js

Question

I am learning GraphQL so I built a little project. Let\'s say I have 2 models, User and Comment.

const Comment = Model.defi         


        

Answer 1

The concept you are refering to is called batching. There are several libraries out there that offer this. For example:

• Dataloader: generic utility maintained by Facebook that provides "a consistent API over various backends and reduce requests to those backends via batching and caching"

• join-monster: "A GraphQL-to-SQL query execution layer for batch data fetching."

Answer 2

To anyone using .NET and the GraphQL for .NET package, I have made an extension method that converts the GraphQL Query into Entity Framework Includes.

public static class ResolveFieldContextExtensions
{
    public static string GetIncludeString(this ResolveFieldContext<object> source)
    {
        return string.Join(',', GetIncludePaths(source.FieldAst));
    }

    private static IEnumerable<Field> GetChildren(IHaveSelectionSet root)
    {
        return root.SelectionSet.Selections.Cast<Field>()
                                           .Where(x => x.SelectionSet.Selections.Any());
    }

    private static IEnumerable<string> GetIncludePaths(IHaveSelectionSet root)
    {
        var q = new Queue<Tuple<string, Field>>();
        foreach (var child in GetChildren(root))
            q.Enqueue(new Tuple<string, Field>(child.Name.ToPascalCase(), child));

        while (q.Any())
        {
            var node = q.Dequeue();
            var children = GetChildren(node.Item2).ToList();
            if (children.Any())
            {
                foreach (var child in children)
                    q.Enqueue(new Tuple<string, Field>
                                  (node.Item1 + "." + child.Name.ToPascalCase(), child));

            }
            else
            {
                yield return node.Item1;
            }
        }}}

Lets say we have the following query:

query {
  getHistory {
    id
    product {
      id
      category {
        id
        subCategory {
          id
        }
        subAnything {
          id
        }
      }
    }
  }
}

We can create a variable in "resolve" method of the field:

var include = context.GetIncludeString();

which generates the following string:

"Product.Category.SubCategory,Product.Category.SubAnything"

and pass it to Entity Framework:

public Task<TEntity> Get(TKey id, string include)
{
    var query = Context.Set<TEntity>();
    if (!string.IsNullOrEmpty(include))
    {
        query = include.Split(',', StringSplitOptions.RemoveEmptyEntries)
                       .Aggregate(query, (q, p) => q.Include(p));
    }
    return query.SingleOrDefaultAsync(c => c.Id.Equals(id));
}