Entity Framework Core 3.1 with Temporal Tables - 访问 SysStartTime 和 SysEndTime

Question

我已经根据 Microsoft SQL 文档创建了临时 tables 创建具有默认历史记录的临时 table 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

迁移：

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");
    }
}

如何设置 Temporal tables 的完整示例：

这非常有效，但现在我想访问 SysStartTime 的值。

我尝试过的：

[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;
            }
        }
    }

和

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

每次迁移都会导致以下结果：

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

这当然会导致 Update-Database 命令出现以下错误：

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

我一直在阅读这两个问题，它似乎一直在 Entity Framework Core 2.2:

尝试禁用隐藏但没有帮助

SQL:

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

Answer 1

对于已经有列的表，我只是删除了迁移的 Up 和 Down 值，然后它起作用了：

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

因为我不想稍后编辑迁移生成的默认代码，所以我决定对新实体这样做：

通常将 DateTime 值添加到迁移：

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;
            }
        }
    }

迁移，如果您已经有 Schema History 然后删除这些行：

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");
    }
}

关于 GitHub 的讨论：

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

Entity Framework Core 3.1 with Temporal Tables - 访问 SysStartTime 和 SysEndTime

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

.net

c#

entity-framework-core

.net-core

temporal-tables