GraphQL queries with tables join using Node.js

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."

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));}