带有临时表的 Entity Framework Core 3.1 - 访问 SysStartTime 和 SysEndTime

本文介绍了带有临时表的 Entity Framework Core 3.1 - 访问 SysStartTime 和 SysEndTime的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我已经根据 Microsoft SQL Docs 创建了时态表使用默认历史记录表创建时态表.

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

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");
    }
}

如何设置临时表的完整示例:

Complete example how Temporal tables was set up:

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

这非常有效，但现在我想访问 SysStartTime 的值.

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

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情况:

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));

这当然会导致 Update-Database 命令出现以下错误:

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

每个表中的列名必须是唯一的.列名 'SysStartTime' 中表 '' 被指定多次.

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

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

Net Core:实体框架和 SQL Server 时态表、自动脚手架

Entity Framework Core 和 SQL Server 2016 时态表

尝试禁用 HIDDEN 但没有帮助

Tried disabling HIDDEN but it did not help

SQL:

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

推荐答案

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:

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));

由于我不想稍后编辑由迁移生成的默认代码，所以我决定对新实体这样做:

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

将 DateTime 值正常添加到迁移中:

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;
            }
        }
    }

迁移，如果您已经有 Schema History，则删除这些行:

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");
    }
}

GitHub 上的讨论:

Discussion on GitHub:

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

这篇关于带有临时表的 Entity Framework Core 3.1 - 访问 SysStartTime 和 SysEndTime的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

ApplicationDBContext