使用MVC5.2中的EntityFramework 6.1.1从现有数据库初始化Code​​-First实体

Question

I have EF6.1.1 installed in a MVC5.2 project (using VS2013). I successfully used code-first to generate the database and I also wrote an initializer with dummy data for testing. For production, I need to load the initial data from an older database on a different server. The table structures are similar but not identical, and the tables have the same names in both databases; I can't use the same models for both.

In addition to the code-first context I have declared a context for the older database, but I don't know what to do with it. Ideally, I would like to pull entities from the old database, then copy field-wise to new entities. If that isn't possible, I'd like to pull rows of old data and somehow populate new entities with the data.

Here is my context declaration for the code-first database:

namespace ITDAccounting.DAL
{
    public class ITDAccountingContext : DbContext
    {
        public DbSet<Department> Departments { get; set; }
        public DbSet<Employee> Employees { get; set; }


        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        }
     }
}

And my context for the old database:

namespace ITDAccounting.DAL
{
    public class BillableUnitsContext : DbContext
    {
// 
    }
}

And some of my initializer code. Obviously, this is bogus data; I want to replace this with code that pulls legit entries from the existing database:

namespace ITDAccounting.DAL
{
    public class ITDAccountingInitializer : DropCreateDatabaseAlways<ITDAccountingContext>
    {
        BillableUnitsContext existingDataContext = new BillableUnitsContext();

        protected override void Seed(ITDAccountingContext context)
        {    
            var employees = new List<Employee>
            {
                new Employee{EffDate=DateTime.Parse("2014-07-01"),Status="A", Number="999001", Wages=96000.00M, Benefits=25000.00M,  Communications=0.0M, Tools=60.0M, TradeMemberships=0.0M, Training=160.0M}
                ,new Employee{EffDate=DateTime.Parse("2014-07-02"),Status="A", Number="999002", Wages=86000.00M, Benefits=25001.00M,  Communications=300.0M, Tools=50.0M, TradeMemberships=10.0M, Training=150.0M}
                ,new Employee{EffDate=DateTime.Parse("2014-07-03"),Status="A", Number="999003", Wages=76000.00M, Benefits=25002.00M,  Communications=40.0M, Tools=40.0M, TradeMemberships=10.0M, Training=140.0M}
                ,new Employee{EffDate=DateTime.Parse("2014-07-04"),Status="A", Number="999004", Wages=66000.00M, Benefits=25003.00M,  Communications=50.0M, Tools=30.0M, TradeMemberships=10.0M, Training=130.0M}
                ,new Employee{EffDate=DateTime.Parse("2014-07-05"),Status="A", Number="999005", Wages=56000.00M, Benefits=25004.00M,  Communications=60.0M, Tools=20.0M, TradeMemberships=10.0M, Training=120.0M}
                ,new Employee{EffDate=DateTime.Parse("2014-07-06"),Status="A", Number="999006", Wages=46000.00M, Benefits=25005.00M,  Communications=750.0M, Tools=10.0M, TradeMemberships=10.0M, Training=110.0M}
             };
        employees.ForEach(e => context.Employees.Add(e));
        context.SaveChanges();

        var departments = new List<Department>
        {
            new Department{ EffDate=DateTime.Parse("2014-07-01"), Status="A", Name="Tacos", Number="999765", Fund="7777", BalanceSheetAccount="44445555", RevenueAccount="11113434"}
            ,new Department{ EffDate=DateTime.Parse("2014-07-02"), Status="A", Name="Burritos", Number="999234", Fund="9080", BalanceSheetAccount="44441111", RevenueAccount="11114545"}
            ,new Department{ EffDate=DateTime.Parse("2014-07-31"), Status="A", Name="BirthdayCake", Number="998754", Fund="1040", BalanceSheetAccount="44442222", RevenueAccount="11116466"}
            ,new Department{ EffDate=DateTime.Parse("2014-07-04"), Status="A", Name="Diet Creme Soda", Number="991234", Fund="0012", BalanceSheetAccount="44443333", RevenueAccount="11112512"}

        };
        departments.ForEach(d => context.Departments.Add(d));
        context.SaveChanges();
    }
}

Thanks in advance for any guidance.

Answer 1

Something like this:

    protected override void Seed(ITDAccountingContext context)
    {
        using (BillableUnitsContext existingDataContext = new BillableUnitsContext())
        {
            var newEmployeeRecords = new List<Employee>();
            foreach (var oldDbEmployee in existingDataContext.Employees.where(e=>MeetsYourSelectionCriteria(e)) 
            {
                newEmployeeRecords.Add(
                    new Employee 
                    {
                        Name = oldDbEmployee.Name, 
                        Rank = oldDbEmployee.Rank, 
                        SerialNo=oldDbEmployee.SerialNo
                    });   
            }

            //similar stuff for departments

        }
        context.Employees.AddRange(newEmployeeRecords);
        context.SaveChanges();
    }

Answer 2

Honestly, how you do this depends on many factors. EF is generally not a good choice for ETL work. Each row you insert creates a larger and larger memory footprint in the local data cache, and it takes a very long time. EF is not designed for bulk operations.

You should probably use something like SSIS, or other dedicated ETL tools.