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[译] EF 6 新特性 - 中

2022-01-18 22:01:44 阅读：191 来源： 互联网

标签：nullable set get Column EF 特性 table public

介绍

接下来我将给大家重点介绍一下.Net 6 之后的一些新的变更，文章都是来自于外国大佬的文章，我这边进行一个翻译，并加上一些自己的理解和解释。

源作者链接：https://blog.okyrylchuk.dev/entity-framework-core-6-features-part-1#heading-1-unicode-attribute

正文

列属性

在模型中使用继承时，您可能对创建的表中的默认 EF Core 列顺序不满意。在 EF Core 6.0 中，您可以使用 ColumnAttribute 指定列顺序。

此外，您可以使用新的 Fluent API - HasColumnOrder()来实现。

public class EntityBase
{
    [Column(Order = 1)]
    public int Id { get; set; }
    [Column(Order = 99)]
    public DateTime UpdatedOn { get; set; }
    [Column(Order = 98)]
    public DateTime CreatedOn { get; set; }
}
public class Person : EntityBase
{
    [Column(Order = 2)]
    public string FirstName { get; set; }
    [Column(Order = 3)]
    public string LastName { get; set; }
    public ContactInfo ContactInfo { get; set; }
}
public class Employee : Person
{
    [Column(Order = 4)]
    public string Position { get; set; }
    [Column(Order = 5)]
    public string Department { get; set; }
}
[Owned]
public class ContactInfo
{
    [Column(Order = 10)]
    public string Email { get; set; }
    [Column(Order = 11)]
    public string Phone { get; set; }
}


迁移：

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.CreateTable(
        name: "Employees",
        columns: table => new
        {
            Id = table.Column<int>(type: "int", nullable: false)
                .Annotation("SqlServer:Identity", "1, 1"),
            FirstName = table.Column<string>(type: "nvarchar(max)", nullable: true),
            LastName = table.Column<string>(type: "nvarchar(max)", nullable: true),
            Position = table.Column<string>(type: "nvarchar(max)", nullable: true),
            Department = table.Column<string>(type: "nvarchar(max)", nullable: true),
            ContactInfo_Email = table.Column<string>(type: "nvarchar(max)", nullable: true),
            ContactInfo_Phone = table.Column<string>(type: "nvarchar(max)", nullable: true),
            CreatedOn = table.Column<DateTime>(type: "datetime2", nullable: false),
            UpdatedOn = table.Column<DateTime>(type: "datetime2", nullable: false)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_Employees", x => x.Id);
        });
}

临时表

EF Core 6.0 支持 SQL Server 时态表。可以将表配置为时间戳和历史表的 SQL Server 默认值的临时表。

public class ExampleContext : DbContext
{
    public DbSet<Person> People { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder
            .Entity<Person>()
            .ToTable("People", b => b.IsTemporal());
    }
    protected override void OnConfiguring(DbContextOptionsBuilder options)
            => options.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=TemporalTables;Trusted_Connection=True;");
}
public class Person 
{ 
    public int Id { get; set; }
    public string Name { get; set; }    
}


迁移：

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.CreateTable(
        name: "People",
        columns: table => new
        {
            Id = table.Column<int>(type: "int", nullable: false)
                .Annotation("SqlServer:Identity", "1, 1"),
            Name = table.Column<string>(type: "nvarchar(max)", nullable: true),
            PeriodEnd = table.Column<DateTime>(type: "datetime2", nullable: false)
                .Annotation("SqlServer:IsTemporal", true)
                .Annotation("SqlServer:TemporalPeriodEndColumnName", "PeriodEnd")
                .Annotation("SqlServer:TemporalPeriodStartColumnName", "PeriodStart"),
            PeriodStart = table.Column<DateTime>(type: "datetime2", nullable: false)
                .Annotation("SqlServer:IsTemporal", true)
                .Annotation("SqlServer:TemporalPeriodEndColumnName", "PeriodEnd")
                .Annotation("SqlServer:TemporalPeriodStartColumnName", "PeriodStart")
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_People", x => x.Id);
        })
        .Annotation("SqlServer:IsTemporal", true)
        .Annotation("SqlServer:TemporalHistoryTableName", "PersonHistory")
        .Annotation("SqlServer:TemporalHistoryTableSchema", null)
        .Annotation("SqlServer:TemporalPeriodEndColumnName", "PeriodEnd")
        .Annotation("SqlServer:TemporalPeriodStartColumnName", "PeriodStart");
}

您可以使用以下方法查询或检索历史数据：

时间AsOf
时间全部
时间从到
时间间隔
时间包含在
使用时态表：

using ExampleContext context = new();
context.People.Add(new() { Name = "Oleg" });
context.People.Add(new() { Name = "Steve" });
context.People.Add(new() { Name = "John" });
await context.SaveChangesAsync();

var people = await context.People.ToListAsync();
foreach (var person in people)
{
    var personEntry = context.Entry(person);
    var validFrom = personEntry.Property<DateTime>("PeriodStart").CurrentValue;
    var validTo = personEntry.Property<DateTime>("PeriodEnd").CurrentValue;
    Console.WriteLine($"Person {person.Name} valid from {validFrom} to {validTo}");
}
// Output:
// Person Oleg valid from 06-Nov-21 17:50:39 PM to 31-Dec-99 23:59:59 PM
// Person Steve valid from 06-Nov-21 17:50:39 PM to 31-Dec-99 23:59:59 PM
// Person John valid from 06-Nov-21 17:50:39 PM to 31-Dec-99 23:59:59 PM

查询历史数据：

var oleg = await context.People.FirstAsync(x => x.Name == "Oleg");
context.People.Remove(oleg);
await context.SaveChangesAsync();
var history = context
                .People
                .TemporalAll()
                .Where(e => e.Name == "Oleg")
                .OrderBy(e => EF.Property<DateTime>(e, "PeriodStart"))
                .Select(
                    p => new
                    {
                        Person = p,
                        PeriodStart = EF.Property<DateTime>(p, "PeriodStart"),
                        PeriodEnd = EF.Property<DateTime>(p, "PeriodEnd")
                    })
                .ToList();
foreach (var pointInTime in history)
{
    Console.WriteLine(
        $"Person {pointInTime.Person.Name} existed from {pointInTime.PeriodStart} to {pointInTime.PeriodEnd}");
}

// Output:
// Person Oleg existed from 06-Nov-21 17:50:39 PM to 06-Nov-21 18:11:29 PM

检索历史数据：

var removedOleg = await context
    .People
    .TemporalAsOf(history.First().PeriodStart)
    .SingleAsync(e => e.Name == "Oleg");

Console.WriteLine($"Id = {removedOleg.Id}; Name = {removedOleg.Name}");
// Output:
// Id = 1; Name = Oleg

稀疏列

EF Core 6.0 支持 SQL Server 稀疏列。它在使用 TPH（每层次表）继承映射时很有用。

public class ExampleContext : DbContext
{
    public DbSet<Person> People { get; set; }
    public DbSet<Employee> Employees { get; set; }
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder
            .Entity<User>()
            .Property(e => e.Login)
            .IsSparse();

        modelBuilder
            .Entity<Employee>()
            .Property(e => e.Position)
            .IsSparse();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
            => options.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=SparseColumns;Trusted_Connection=True;");
}

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}
public class User : Person
{
    public string Login { get; set; }
}
public class Employee : Person
{
    public string Position { get; set; }
}


迁移：


protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.CreateTable(
        name: "People",
        columns: table => new
        {
            Id = table.Column<int>(type: "int", nullable: false)
                .Annotation("SqlServer:Identity", "1, 1"),
            Name = table.Column<string>(type: "nvarchar(max)", nullable: false),
            Discriminator = table.Column<string>(type: "nvarchar(max)", nullable: false),
            Position = table.Column<string>(type: "nvarchar(max)", nullable: true)
                .Annotation("SqlServer:Sparse", true),
            Login = table.Column<string>(type: "nvarchar(max)", nullable: true)
                .Annotation("SqlServer:Sparse", true)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_People", x => x.Id);
        });
}

结语

联系作者：加群：867095512 @MrChuJiu

公众号

标签：nullable,set,get,Column,EF,特性,table,public
来源： https://www.cnblogs.com/MrChuJiu/p/15820031.html

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[译] EF 6 新特性 - 中

介绍

正文

列属性

临时表

稀疏列

结语