http://www.zzzprojects.com/entity-framework-how-to-bulk-insert-in-sql-server/

entity-framework-how-to-bulk-insert-in-sql-server-all.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;

namespace Z.EntityFramework.Extensions
{
    public class HowTo_BulkInsert_InSqlServer
    {
        public const int BatchSize = 4000;
        public const string ConnectionString = @"Server=XPS8700;Initial Catalog=Z.Test.EntityFramework.Plus.EF6;Integrated Security=True;";
        internal const string InsertStagingTable = @"MERGE INTO EntitySimples AS DestinationTable
USING
(
{StagingTable}
) AS StagingTable
ON 1 = 2
WHEN NOT MATCHED THEN
    INSERT ( ColumnInt )
    VALUES ( ColumnInt )
;";
        internal const string InsertStagingTableWithOutput = @"MERGE INTO EntitySimples AS DestinationTable
USING
(
    SELECT ZZZ_Index, ColumnInt FROM {TemporaryTable} WHERE ZZZ_Index >= @IndexStart AND ZZZ_Index < @IndexEnd
) AS StagingTable
ON 1 = 2
WHEN NOT MATCHED THEN
    INSERT ( ColumnInt )
    VALUES ( ColumnInt )
OUTPUT
    StagingTable.ZZZ_Index,
    INSERTED.ID
;";

        public static void Test()
        {
            var list1 = GenerateItems(9);
            var list2 = GenerateItems(10);
            var list3 = GenerateItems(10);

            BulkInsert(list1);
            BulkInsert(list2);
            BulkInsert(list3, true);
        }

        public static List<EntitySimple> GenerateItems(int count)
        {
            var list = new List<EntitySimple>();

            for (var i = 0; i < count; i++)
            {
                list.Add(new EntitySimple {ColumnInt = i});
            }

            return list;
        }

        public static void BulkInsert(List<EntitySimple> list, bool outputIdentity = false)
        {
            if (outputIdentity)
            {
                BulkInsertTemporaryTable(list);
            }
            else if (list.Count >= 10)
            {
                BulkInsertBulkCopy(list);
            }
            else
            {
                BulkInsertSqlCommand(list);
            }
        }

        private static void BulkInsertSqlCommand(List<EntitySimple> list)
        {
            // CREATE sql derived table
            var sqlDerivedTable = "SELECT " + string.Join(" UNION SELECT ", list.Select((simple, i) => "@" + i + " AS ColumnInt"));

            using (var connection = new SqlConnection(ConnectionString))
            {
                connection.Open();

                using (var command = new SqlCommand(InsertStagingTable.Replace("{StagingTable}", sqlDerivedTable), connection))
                {
                    // ADD parameter
                    for (var i = 0; i < list.Count; i++)
                    {
                        command.Parameters.AddWithValue("@" + i, list[i].ColumnInt);
                    }

                    command.ExecuteNonQuery();
                }
            }
        }

        private static void BulkInsertBulkCopy(List<EntitySimple> list)
        {
            var dt = ToDataTable(list);

            using (var connection = new SqlConnection(ConnectionString))
            {
                connection.Open();

                using (var bulkCopy = new SqlBulkCopy(connection, SqlBulkCopyOptions.CheckConstraints | SqlBulkCopyOptions.FireTriggers, null))
                {
                    bulkCopy.BatchSize = BatchSize;
                    bulkCopy.ColumnMappings.Add("ColumnInt", "ColumnInt");
                    bulkCopy.DestinationTableName = "EntitySimples";
                    bulkCopy.WriteToServer(dt);
                }
            }
        }

        private static void BulkInsertTemporaryTable(List<EntitySimple> list)
        {
            var dt = ToDataTable(list);
            var temporaryTable = "#" + Guid.NewGuid().ToString().Replace("-", "_");

            using (var connection = new SqlConnection(ConnectionString))
            {
                connection.Open();

                // CREATE temporary table
                using (var command = new SqlCommand("CREATE TABLE " + temporaryTable + " (ZZZ_Index INT, ColumnInt INT)", connection))
                {
                    command.ExecuteNonQuery();
                }

                // INSERT INTO temporary table
                using (var bulkCopy = new SqlBulkCopy(connection, SqlBulkCopyOptions.CheckConstraints | SqlBulkCopyOptions.FireTriggers, null))
                {
                    bulkCopy.BatchSize = BatchSize;
                    bulkCopy.ColumnMappings.Add("ZZZ_Index", "ZZZ_Index");
                    bulkCopy.ColumnMappings.Add("ColumnInt", "ColumnInt");
                    bulkCopy.DestinationTableName = temporaryTable;
                    bulkCopy.WriteToServer(dt);
                }

                // INSERT INTO destination FROM temporary table
                var currentIndex = 0;
                while (currentIndex < list.Count)
                {
                    using (var command = new SqlCommand(InsertStagingTableWithOutput.Replace("{TemporaryTable}", temporaryTable), connection))
                    {
                        command.Parameters.AddWithValue(@"IndexStart", currentIndex);
                        command.Parameters.AddWithValue("@IndexEnd", currentIndex + BatchSize);

                        var dtOutput = new DataTable();
                        using (var adapter = new SqlDataAdapter(command))
                        {
                            adapter.Fill(dtOutput);
                        }

                        // OUTPUT value
                        foreach (DataRow dr in dtOutput.Rows)
                        {
                            var index = Convert.ToInt32(dr["ZZZ_Index"]);
                            list[index].ID = Convert.ToInt32(dr["ID"]);
                        }
                    }

                    currentIndex += BatchSize;
                }
            }
        }

        public static DataTable ToDataTable(List<EntitySimple> list)
        {
            // CREATE table
            var dt = new DataTable();

            // ADD columns
            dt.Columns.Add("ZZZ_Index", typeof (int));
            dt.Columns.Add("ColumnInt", typeof (int));

            // ADD rows
            for (var i = 0; i < list.Count; i++)
            {
                dt.Rows.Add(i, list[i].ColumnInt);
            }

            return dt;
        }

        public class EntitySimple
        {
            public int ID { get; set; }
            public int ColumnInt { get; set; }
        }
    }
}