Entity Framework Core 3.1 with Temporal Tables - Access SysStartTime and SysEndTime

问题

I have created temporal tables based on Microsoft SQL Docs Creating a temporal table with a default history table.

https://docs.microsoft.com/en-us/sql/relational-databases/tables/creating-a-system-versioned-temporal-table?view=sql-server-ver15#creating-a-temporal-table-with-a-default-history-table

Migration:

public partial class Temporaltables : Migration
{
    List<string> tablesToUpdate = new List<string>
        {
           "Images",
           "Languages",
           "Questions",
           "Texts",
           "Medias",
        };

    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.Sql($"CREATE SCHEMA History");
        foreach (var table in tablesToUpdate)
        {
            string alterStatement = $@"ALTER TABLE [{table}] ADD SysStartTime datetime2(0) GENERATED ALWAYS AS ROW START HIDDEN
     CONSTRAINT DF_{table}_SysStart DEFAULT GETDATE(), SysEndTime datetime2(0) GENERATED ALWAYS AS ROW END HIDDEN
     CONSTRAINT DF_{table}_SysEnd DEFAULT CONVERT(datetime2 (0), '9999-12-31 23:59:59'),
     PERIOD FOR SYSTEM_TIME (SysStartTime, SysEndTime)";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE = History.[{table}]));";
            migrationBuilder.Sql(alterStatement);
        }
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        foreach (var table in tablesToUpdate)
        {
            string alterStatement = $@"ALTER TABLE [{table}] SET (SYSTEM_VERSIONING = OFF);";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] DROP PERIOD FOR SYSTEM_TIME";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] DROP DF_{table}_SysStart, DF_{table}_SysEnd";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] DROP COLUMN SysStartTime, COLUMN SysEndTime";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"DROP TABLE History.[{table}]";
            migrationBuilder.Sql(alterStatement);
        }
        migrationBuilder.Sql($"DROP SCHEMA History");
    }
}

Complete example how Temporal tables was set up:

https://stackoverflow.com/a/64244548/3850405

This works really well but now I want to access the value for SysStartTime.

What I have tried:

[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public DateTime SysStartTime { get; set; }

ApplicationDbContext.cs:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{...

    foreach (var et in modelBuilder.Model.GetEntityTypes())
    {
        foreach (var prop in et.GetProperties())
        {
            if (prop.Name == "SysStartTime" || prop.Name == "SysEndTime")
            {
                prop.ValueGenerated = Microsoft.EntityFrameworkCore.Metadata.ValueGenerated.OnAddOrUpdate;
            }
        }
    }

and

modelBuilder.Entity<Question>(e =>
{
    e.Property(p => p.SysStartTime).ValueGeneratedOnAddOrUpdate();
});

Every migration leads to the following:

migrationBuilder.AddColumn<DateTime>(
    name: "SysStartTime",
    table: "Questions",
    type: "datetime2(0)",
    nullable: false,
    defaultValue: new DateTime(1, 1, 1, 0, 0, 0, 0, DateTimeKind.Unspecified));

This of course leads to the error below on Update-Database command:

Column names in each table must be unique. Column name 'SysStartTime' in table '' is specified more than once.

I have been reading both these questions and it seems to have been working in Entity Framework Core 2.2:

Net Core: Entity Framework and SQL Server Temporal Tables, Automatic Scaffolding

Entity Framework Core and SQL Server 2016 temporal tables

Tried disabling HIDDEN but it did not help

SQL:

ALTER TABLE [dbo].Questions ALTER COLUMN SysStartTime DROP HIDDEN;

回答1:

For tables that already had the columns I simply removed Up and Down values for the migration and then it worked:

migrationBuilder.AddColumn<DateTime>(
    name: "SysStartTime",
    table: "Questions",
    type: "datetime2(0)",
    nullable: false,
    defaultValue: new DateTime(1, 1, 1, 0, 0, 0, 0, DateTimeKind.Unspecified));

Since I do not want to edit default code generated by migrations later on I decided to do it like this for new entities:

Add DateTime values normally to migration:

public DateTime SysStartTime { get; set; }

public DateTime SysEndTime { get; set; }

ApplicationDbContext.cs:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{...

    foreach (var et in modelBuilder.Model.GetEntityTypes())
    {
        foreach (var prop in et.GetProperties())
        {
            if (prop.Name == "SysStartTime" || prop.Name == "SysEndTime")
            {
                prop.ValueGenerated = Microsoft.EntityFrameworkCore.Metadata.ValueGenerated.OnAddOrUpdate;
            }
        }
    }

Migration, if you already have Schema History then remove those rows:

public partial class Temporaltables : Migration
{
    List<string> tablesToUpdate = new List<string>
        {
           "NewTable1",
           "NewTable2",
        };

    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.Sql($"CREATE SCHEMA History");
        foreach (var table in tablesToUpdate)
        {
            string alterStatement = $@"ALTER TABLE [{table}] 
                ADD PERIOD FOR SYSTEM_TIME ([SysStartTime], [SysEndTime])";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] 
                SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE = History.[{table}], DATA_CONSISTENCY_CHECK = ON));";
            migrationBuilder.Sql(alterStatement);
        }
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        foreach (var table in tablesToUpdate)
        {
            string alterStatement = $@"ALTER TABLE [{table}] SET (SYSTEM_VERSIONING = OFF);";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"ALTER TABLE [{table}] DROP PERIOD FOR SYSTEM_TIME";
            migrationBuilder.Sql(alterStatement);
            alterStatement = $@"DROP TABLE History.[{table}]";
            migrationBuilder.Sql(alterStatement);
        }
        migrationBuilder.Sql($"DROP SCHEMA History");
    }
}

Discussion on GitHub:

https://github.com/dotnet/efcore/issues/23184

来源：https://stackoverflow.com/questions/64653497/entity-framework-core-3-1-with-temporal-tables-access-sysstarttime-and-sysendt