Added a full sample interceptor page

doc/index.md

@@ -42,6 +42,8 @@ Example use cases:
 - Preventing accidental insertion of DateTime values having ```DateTimeKind.Unspecified```.
 - Forcing all postgres date/time types to be returned to Entity Framework as ```DateTimeOffset```.
 
+[Here is an example of a fully implemented EF6 interceptor](sample-interceptor.md)
+
 ```c#
 [DbConfigurationType(typeof(AppDbContextConfiguration))]
 public class AppDbContext : DbContext

doc/sample-interceptor.md

@@ -0,0 +1,335 @@
+### Sample Entity Framework 6 Interceptor ###
+
+The following is a sample interceptor class that forces all returned date/time types from Npgsql to be converted to UTC (if local) or specified as being UTC (if ```DateTimeKind.Unknown```).
+
+```c#
+using System;
+using System.Collections;
+using System.Data;
+using System.Data.Common;
+using System.Data.Entity.Infrastructure.Interception;
+using System.IO;
+using System.Runtime.Remoting;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace My.Interceptors
+{
+    class EnforceDateTimeUtcInterceptor : DbCommandInterceptor
+    {
+        public override void NonQueryExecuting(
+            DbCommand command,
+            DbCommandInterceptionContext<int> interceptionContext)
+        {
+            EnsureThatAllDateTimePropertiesAreUtc(command.Parameters);
+        }
+
+        public override void ReaderExecuting(
+            DbCommand command,
+            DbCommandInterceptionContext<DbDataReader> interceptionContext)
+        {
+            EnsureThatAllDateTimePropertiesAreUtc(command.Parameters);
+        }
+
+        public override void ScalarExecuting(
+            DbCommand command,
+            DbCommandInterceptionContext<object> interceptionContext)
+        {
+            EnsureThatAllDateTimePropertiesAreUtc(command.Parameters);
+        }
+
+        public override void ReaderExecuted(
+            DbCommand command,
+            DbCommandInterceptionContext<DbDataReader> interceptionContext)
+        {
+            if (interceptionContext.Result == null) return;
+            interceptionContext.Result = new EnforcingDbDataReader(interceptionContext.Result);
+        }
+
+        public override void ScalarExecuted(
+            DbCommand command,
+            DbCommandInterceptionContext<object> interceptionContext)
+        {
+            interceptionContext.Result = ConvertToUtcOrReturn(interceptionContext.Result);
+        }
+
+        static void EnsureThatAllDateTimePropertiesAreUtc(DbParameterCollection parameters)
+        {
+            if (parameters == null) throw new ArgumentNullException(nameof(parameters));
+
+            foreach (DbParameter parameter in parameters)
+            {
+                var dateTime = parameter.Value as DateTime?;
+                if (dateTime != null && dateTime.Value != DateTime.MinValue && dateTime.Value.Kind != DateTimeKind.Utc)
+                {
+                    throw new InvalidOperationException(
+                        $"Parameter '{parameter.ParameterName}' must have a Utc value. A value of {dateTime.Value.Kind} was found instead.");
+                }
+
+                var dateTimeOffset = parameter.Value as DateTimeOffset?;
+                if (dateTimeOffset != null && dateTimeOffset.Value.Offset != TimeSpan.Zero)
+                {
+                    throw new InvalidOperationException(
+                        $"Parameter '{parameter.ParameterName}' must have a Utc value. An offset of {dateTimeOffset.Value.Offset} was found instead.");
+                }
+            }
+        }
+
+        static object ConvertToUtcOrReturn(object obj)
+        {
+            if (obj == null) return null;
+
+            var dateTime = obj as DateTime?;
+            if (dateTime != null)
+            {
+                return ConvertToUtc(dateTime.Value);
+            }
+
+            var dateTimeOffset = obj as DateTimeOffset?;
+            if (dateTimeOffset != null)
+            {
+                return dateTimeOffset.Value.ToUniversalTime();
+            }
+
+            return obj;
+        }
+
+        static DateTime ConvertToUtc(DateTime dateTime)
+        {
+            if (dateTime == DateTime.MinValue) return dateTime;
+
+            return dateTime.Kind == DateTimeKind.Local
+                ? dateTime.ToUniversalTime()
+                : DateTime.SpecifyKind(dateTime, DateTimeKind.Utc);
+        }
+
+        class EnforcingDbDataReader : DbDataReader, IDataReader
+        {
+            readonly DbDataReader _reader;
+
+            public override int Depth => this._reader.Depth;
+            public override int FieldCount => this._reader.FieldCount;
+            public override bool HasRows => this._reader.HasRows;
+            public override bool IsClosed => this._reader.IsClosed;
+            public override int RecordsAffected => this._reader.RecordsAffected;
+            public override int VisibleFieldCount => this._reader.VisibleFieldCount;
+            public override object this[string name] => ConvertToUtcOrReturn(this._reader[name]);
+            public override object this[int ordinal] => ConvertToUtcOrReturn(this._reader[ordinal]);
+
+            public EnforcingDbDataReader(DbDataReader reader)
+            {
+                if (reader == null) throw new ArgumentNullException(nameof(reader));
+                this._reader = reader;
+            }
+
+            public override void Close()
+            {
+                this._reader.Close();
+            }
+
+            public override ObjRef CreateObjRef(Type requestedType)
+            {
+                return this._reader.CreateObjRef(requestedType);
+            }
+
+            public override bool GetBoolean(int ordinal)
+            {
+                return this._reader.GetBoolean(ordinal);
+            }
+
+            public override byte GetByte(int ordinal)
+            {
+                return this._reader.GetByte(ordinal);
+            }
+
+            public override long GetBytes(int ordinal, long dataOffset, byte[] buffer, int bufferOffset, int length)
+            {
+                return this._reader.GetBytes(ordinal, dataOffset, buffer, bufferOffset, length);
+            }
+
+            public override char GetChar(int ordinal)
+            {
+                return this._reader.GetChar(ordinal);
+            }
+
+            public override long GetChars(int ordinal, long dataOffset, char[] buffer, int bufferOffset, int length)
+            {
+                return this._reader.GetChars(ordinal, dataOffset, buffer, bufferOffset, length);
+            }
+
+            IDataReader IDataRecord.GetData(int i)
+            {
+                return ((IDataRecord)this._reader).GetData(i);
+            }
+
+            public override string GetDataTypeName(int ordinal)
+            {
+                return this._reader.GetDataTypeName(ordinal);
+            }
+
+            public override DateTime GetDateTime(int ordinal)
+            {
+                return ConvertToUtc(this._reader.GetDateTime(ordinal));
+            }
+
+            public override decimal GetDecimal(int ordinal)
+            {
+                return this._reader.GetDecimal(ordinal);
+            }
+
+            public override double GetDouble(int ordinal)
+            {
+                return this._reader.GetDouble(ordinal);
+            }
+
+            public override IEnumerator GetEnumerator()
+            {
+                return this._reader.GetEnumerator();
+            }
+
+            public override Type GetFieldType(int ordinal)
+            {
+                return this._reader.GetFieldType(ordinal);
+            }
+
+            public override T GetFieldValue<T>(int ordinal)
+            {
+                return (T)ConvertToUtcOrReturn(this._reader.GetFieldValue<T>(ordinal));
+            }
+
+            public override async Task<T> GetFieldValueAsync<T>(int ordinal, CancellationToken cancellationToken)
+            {
+                return (T)ConvertToUtcOrReturn(
+                    await this._reader
+                        .GetFieldValueAsync<T>(ordinal, cancellationToken)
+                        .ConfigureAwait(true));
+            }
+
+            public override float GetFloat(int ordinal)
+            {
+                return this._reader.GetFloat(ordinal);
+            }
+
+            public override Guid GetGuid(int ordinal)
+            {
+                return this._reader.GetGuid(ordinal);
+            }
+
+            public override short GetInt16(int ordinal)
+            {
+                return this._reader.GetInt16(ordinal);
+            }
+
+            public override int GetInt32(int ordinal)
+            {
+                return this._reader.GetInt32(ordinal);
+            }
+
+            public override long GetInt64(int ordinal)
+            {
+                return this._reader.GetInt64(ordinal);
+            }
+
+            public override string GetName(int ordinal)
+            {
+                return this._reader.GetName(ordinal);
+            }
+
+            public override int GetOrdinal(string name)
+            {
+                return this._reader.GetOrdinal(name);
+            }
+
+            public override Type GetProviderSpecificFieldType(int ordinal)
+            {
+                return this._reader.GetProviderSpecificFieldType(ordinal);
+            }
+
+            public override object GetProviderSpecificValue(int ordinal)
+            {
+                return ConvertToUtcOrReturn(this._reader.GetProviderSpecificValue(ordinal));
+            }
+
+            public override int GetProviderSpecificValues(object[] values)
+            {
+                var result = this._reader.GetProviderSpecificValues(values);
+                for (int i = 0; i < values.Length; i++)
+                {
+                    values[i] = ConvertToUtcOrReturn(values[i]);
+                }
+                return result;
+            }
+
+            public override DataTable GetSchemaTable()
+            {
+                return this._reader.GetSchemaTable();
+            }
+
+            public override Stream GetStream(int ordinal)
+            {
+                return this._reader.GetStream(ordinal);
+            }
+
+            public override string GetString(int ordinal)
+            {
+                return this._reader.GetString(ordinal);
+            }
+
+            public override TextReader GetTextReader(int ordinal)
+            {
+                return this._reader.GetTextReader(ordinal);
+            }
+
+            public override object GetValue(int ordinal)
+            {
+                return ConvertToUtcOrReturn(this._reader.GetValue(ordinal));
+            }
+
+            public override int GetValues(object[] values)
+            {
+                var result = this._reader.GetValues(values);
+                for (int i = 0; i < values.Length; i++)
+                {
+                    values[i] = ConvertToUtcOrReturn(values[i]);
+                }
+                return result;
+            }
+
+            public override object InitializeLifetimeService()
+            {
+                return this._reader.InitializeLifetimeService();
+            }
+
+            public override bool IsDBNull(int ordinal)
+            {
+                return this._reader.IsDBNull(ordinal);
+            }
+
+            public override Task<bool> IsDBNullAsync(int ordinal, CancellationToken cancellationToken)
+            {
+                return this._reader.IsDBNullAsync(ordinal, cancellationToken);
+            }
+
+            public override bool NextResult()
+            {
+                return this._reader.NextResult();
+            }
+
+            public override Task<bool> NextResultAsync(CancellationToken cancellationToken)
+            {
+                return this._reader.NextResultAsync(cancellationToken);
+            }
+
+            public override bool Read()
+            {
+                return this._reader.Read();
+            }
+
+            public override Task<bool> ReadAsync(CancellationToken cancellationToken)
+            {
+                return this._reader.ReadAsync(cancellationToken);
+            }
+        }
+    }
+}
+```