Global resource-specific metadata

DESCRIPTION

As of today, there are two ways to define metadata. Either global (once per response) or per resource (for each item in the result the metadata is added).

If we add the metadata per resource we can easily gather additional information about the entity by accessing the generic type information via reflection. Unfortunately this seems not possible if using the global metadata, because the interface IResponseMeta is lacking the type information.

ACTUAL BEHAVIOR

Consider the following entity, which contains additional attributes which are used to generate meta data.

public sealed class SupportTicket : Identifiable
{
    [Attr]
    [Required]
    [MaxLength(200)]
    public string Description { get; set; }
}

The only way to include those metadata is by creating a ResourceDefinition inherit from JsonApiResourceDefinition<SupportTicket> which then allows us to override IDictionary<string, object> GetMeta(SupportTicket resource). This allows us to create something like this:

{
    "links": {
        "self": "http://localhost/supportTickets",
        "first": "http://localhost/supportTickets"
    },
    "data": [
        {
            "type": "supportTickets",
            "id": "1",
            "attributes": {
                "description": "Critical: Quae magnam est modi quaerat voluptas repellendus quos dolorem. Ipsum rerum voluptatem facere. Veniam dolor soluta repudiandae doloribus. Qui ratione soluta velit deleniti atque id ad dicta sint."
            },
            "links": {
                "self": "http://localhost/supportTickets/1"
            },
            "meta": {
                "rules": [
                    "required": "true",
                    "maxLength": "200" 
                ]
            }
        }, {
            "type": "supportTickets",
            "id": "2",
            "attributes": {
                "description": "Lorem ipsum dolor sit....."
            },
            "links": {
                "self": "http://localhost/supportTickets/2"
            },
            "meta": {
                "rules": [
                    "required": "true",
                    "maxLength": "200" 
                ]
            }
        }
    ]
}

Even though this generally works, the data sent to the client is highly redundant.

EXPECTED BEHAVIOR

We need a way to create entity related global meta data which leads to the following result:

{
    "links": {
        "self": "http://localhost/supportTickets",
        "first": "http://localhost/supportTickets",
        "meta": {
            "rules": [
                "required": "true",
                "maxLength": "200" 
            ]
        }
    },
    "data": [
        {
            "type": "supportTickets",
            "id": "1",
            "attributes": {
                "description": "Critical: Quae magnam est modi quaerat voluptas repellendus quos dolorem. Ipsum rerum voluptatem facere. Veniam dolor soluta repudiandae doloribus. Qui ratione soluta velit deleniti atque id ad dicta sint."
            },
            "links": {
                "self": "http://localhost/supportTickets/1"
            }
        }, {
            "type": "supportTickets",
            "id": "2",
            "attributes": {
                "description": "Lorem ipsum dolor sit....."
            },
            "links": {
                "self": "http://localhost/supportTickets/2"
            }
        }
    ]
}

For some reason this feature seemed to be remove in PR: https://github.com/json-api-dotnet/JsonApiDotNetCore/pull/845/files

[bart-degreed]

If I understand you correctly, you’d like to add top-level meta to GET resource requests that lists the attr validation rules for the resource type being requested. To accomplish that, inject IJsonApiRequest in your IResponseMeta implementation and make sure to register it request-scoped.

Example:

public sealed class SupportTicket : Identifiable
{
    [Attr]
    [Required]
    [MaxLength(100)]
    public string Description { get; set; }

    [Attr]
    [MaxLength(25)]
    public string Other { get; set; }
}

public sealed class SupportResponseMeta : IResponseMeta
{
    private readonly IJsonApiRequest _request;

    public SupportResponseMeta(IJsonApiRequest request)
    {
        _request = request;
    }

    public IReadOnlyDictionary<string, object> GetMeta()
    {
        if (!_request.IsReadOnly || _request.Kind == EndpointKind.Relationship)
        {
            return null;
        }

        IDictionary<string, IDictionary<string, string>> rules = new Dictionary<string, IDictionary<string, string>>();

        ResourceContext resourceContext = _request.SecondaryResource ?? _request.PrimaryResource;

        foreach (AttrAttribute attrAttribute in resourceContext.Attributes)
        {
            IDictionary<string, string> attributeRules = GetAttributeRules(attrAttribute);

            if (attributeRules.Any())
            {
                rules.Add(attrAttribute.PublicName, attributeRules);
            }
        }

        return rules.Any()
            ? new Dictionary<string, object>
            {
                ["rules"] = rules
            }
            : null;
    }

    private static IDictionary<string, string> GetAttributeRules(AttrAttribute attrAttribute)
    {
        var attributeRules = new Dictionary<string, string>();

        foreach (Attribute attribute in attrAttribute.Property.GetCustomAttributes())
        {
            string ruleName = null;
            string ruleValue = null;

            if (attribute is RequiredAttribute)
            {
                ruleName = "required";
                ruleValue = "true";
            }
            else if (attribute is MaxLengthAttribute maxLengthAttribute)
            {
                ruleName = "maxLength";
                ruleValue = maxLengthAttribute.Length.ToString();
            }
            // ...

            if (ruleName != null)
            {
                attributeRules.Add(ruleName, ruleValue);
            }
        }

        return attributeRules;
    }
}

which produces:

{
  "meta": {
    "rules": {
      "description": {
        "required": "true",
        "maxLength": "100"
      },
      "other": {
        "maxLength": "25"
      }
    }
  },
  "links": {
    "self": "http://localhost/supportTickets",
    "first": "http://localhost/supportTickets"
  },
  "data": []
}

[bart-degreed]

The general hint was added to the docs recently, but it hasn’t been merged yet. See https://github.com/json-api-dotnet/JsonApiDotNetCore/blob/write-callbacks/docs/usage/extensibility/middleware.md.