edmx builder

edmx.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml;
using Microsoft.AspNet.OData.Builder;
using Microsoft.OData.Edm.Csdl;
using Microsoft.OData.Edm.Validation;

namespace foooo.Api.Odata
{
    /// <summary>
    /// Used to generate edmx metadata for Odata endpoints that are not handled by OData frameworks,
    /// but by manually conmforming to the standard.
    /// </summary>
    public class CachedEdmxBuilder<T> where T : class
    {
        private readonly Lazy<string> _entityModel;

        public CachedEdmxBuilder(string entityModelName)
        {
            _entityModel = new Lazy<string>(() => GenerateEdmx(entityModelName), true);
        }

        /// <summary>
        /// Lazily return the OData model for samples pr day
        /// </summary>
        public string GetEdmx()
        {
            return _entityModel.Value;
        }

        private class Utf8StringWriter : StringWriter
        {
            public override Encoding Encoding => new UTF8Encoding(false);
        }

        /// <summary>
        /// This is probably a bit expensive as it is using reflection and building up a model dynamically.
        /// Therefore we cache it and do not expose it to the outside.
        /// </summary>
        private static string GenerateEdmx(string entitySetName)
        {
            var builder = new ODataConventionModelBuilder();
            var typeOfModel = typeof(T);
            builder.Namespace = typeOfModel.Namespace;
            builder.EntitySet<T>(entitySetName);
            builder.DataServiceVersion = new Version(4, 0);

            var samplesModel = builder.GetEdmModel();

            using (var stringWriter = new Utf8StringWriter())
            {
                using (var xmlWriter = XmlWriter.Create(stringWriter))
                {
                    IEnumerable<EdmError> edmErrors;
                    xmlWriter.WriteStartDocument();
                    xmlWriter.WriteStartElement("edmx", "Edmx", "http://docs.oasis-open.org/odata/ns/edmx");
                    xmlWriter.WriteAttributeString("", "Version", "", "4.0");
                    xmlWriter.WriteStartElement("edmx", "DataServices", "http://docs.oasis-open.org/odata/ns/edmx");

                    var res = samplesModel.TryWriteSchema(xmlWriter, out edmErrors);
                    var edmErrorResult = edmErrors.ToList();
                    if (edmErrorResult.Count > 0 || !res)
                    {
                        throw new Exception(
                            $"Could not generate edmx model, {edmErrorResult.SelectMany(e => e.ErrorMessage.ToString())}");
                    }
                    xmlWriter.WriteEndElement();
                    xmlWriter.WriteEndElement();
                    xmlWriter.Flush();
                    return stringWriter.ToString();
                }
            }
        }
    }
}