EF Core 6 新功能匯總（四）

在這篇文章中，你將看到 EF Core 對(duì) SQLite、In-memory 提供者和 EF.Functions.Contains 方法的改進(jìn)。

這是 EF Core 6 新功能匯總的第四篇文章：

• EF Core 6 新功能匯總（一）

• EF Core 6 新功能匯總（二）

• EF Core 6 新功能匯總（三）

• EF Core 6 新功能匯總（四）

1SQLite 支持 DateOnly 和 TimeOnly

在 EF Core 6.0 中，SQLite 提供者支持新的 DateOnly 和 TimeOnly 類型。它將它們存儲(chǔ)為 TEXT。

using?var context = new ExampleContext();

var query1 = context.People
    .Where(p => p.Birthday < new DateOnly(2000, 1, 1))
    .ToQueryString();

Console.WriteLine(query1);
// SELECT "p"."Id", "p"."Birthday", "p"."Name"
// FROM "People" AS "p"
// WHERE "p"."Birthday" < '2000-01-01'

var query2 = context.Notifications
    .Where(n => n.AllowedFrom >= new TimeOnly(8, 0) && n.AllowedTo <= new TimeOnly(16, 0))
    .ToQueryString();

Console.WriteLine(query2);
// SELECT "n"."Id", "n"."AllowedFrom", "n"."AllowedTo"
// FROM "Notifications" AS "n"
// WHERE("n"."AllowedFrom" >= '08:00:00') AND("n"."AllowedTo" <= '16:00:00')

class?Person
{
    public?int Id { get; set; }
    public?string Name { get; set; }
    public DateOnly Birthday { get; set; }
}
class?Notification
{
    public?int Id { get; set; }
    public TimeOnly AllowedFrom { get; set; }
    public TimeOnly AllowedTo { get; set; }
}
class?ExampleContext : DbContext
{
    public DbSet People { get; set; }
    public DbSet Notifications { get; set; }

    protected?override?void?OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlite(@"Data Source=Db\DateOnlyTimeOnly.db");
}

2SQLite 連接是池化的

SQLite 數(shù)據(jù)庫(kù)是一個(gè)文件。因此，在大多數(shù)情況下，創(chuàng)建一個(gè)連接是很快的。然而，打開一個(gè)加密數(shù)據(jù)庫(kù)的連接會(huì)非常慢。因此，在 EF Core 6 中，SQLite 連接現(xiàn)在是池化的，就像其他數(shù)據(jù)庫(kù)提供者一樣。

class?Person
{
    public?int Id { get; set; }
    public?string Name { get; set; }
}
class?ExampleContext : DbContext
{
    public DbSet People { get; set; }

    protected?override?void?OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlite("Data Source=EncryptedDb.db;Mode=ReadWriteCreate;Password=password");
}

3SQLite 中的命令超時(shí)

在 EF Core 6 的 SQLite 中，支持添加 Command Timeout 命令到連接字符串中，你可以用它來指定 SQLite 的默認(rèn)超時(shí)時(shí)間。

class?Person
{
    public?int Id { get; set; }
    public?string Name { get; set; }
}
class?ExampleContext : DbContext
{
    public DbSet People { get; set; }

    // 60 seconds as the default timeout for commands created by connection
    protected?override?void?OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlite("Data Source=Test.db;Command Timeout=60");
}

4SQLite 中的保存點(diǎn)

在 EF Core 6.0 中，SQLite 支持保存點(diǎn)(Savepoints)。你可以保存、回滾和釋放保存點(diǎn)。

var dbPath = Path.GetFullPath(Path.Combine(AppContext.BaseDirectory, "..\\..\\..\\Savepoints.db"));

using?var connection = new SqliteConnection($"Data Source={dbPath}");
connection.Open();
using?var transaction = connection.BeginTransaction();

// The insert is committed to the database
using (var command = connection.CreateCommand())
{
    command.CommandText = @"INSERT INTO People (Name) VALUES ('Oleg')";
    command.ExecuteNonQuery();
}

transaction.Save("MySavepoint");

// The update is not commited since savepoint is rolled back before commiting the transaction
using (var command = connection.CreateCommand())
{
    command.CommandText = @"UPDATE People SET Name = 'Not Oleg' WHERE Id = 1";
    command.ExecuteNonQuery();
}

transaction.Rollback("MySavepoint");
transaction.Commit();

5內(nèi)存數(shù)據(jù)庫(kù)驗(yàn)證必需屬性

在 EF Core 6.0 中，內(nèi)存(In-memory)數(shù)據(jù)庫(kù)驗(yàn)證了必需（In-momory）的屬性。如果你試圖保存一個(gè)實(shí)體的必需屬性值為空，就會(huì)出現(xiàn)異常。如果有必要，你可以禁用這個(gè)驗(yàn)證。

using?var context = new ExampleContext();

var blog = new Blog();
context.Blogs.Add(blog);

await context.SaveChangesAsync();
// Unhandled exception. Microsoft.EntityFrameworkCore.DbUpdateException:
// Required properties '{'Title'}' are missing for the instance of entity
// type 'Blog' with the key value '{Id: 1}'.

class?Blog
{
    public?int Id { get; set; }
    [Required]
    public?string Title { get; set; }
}
class?ExampleContext : DbContext
{
    public DbSet Blogs { get; set; }

    protected?override?void?OnConfiguring(DbContextOptionsBuilder options)
        => options
        .EnableSensitiveDataLogging()
        .LogTo(Console.WriteLine, new[] { InMemoryEventId.ChangesSaved })
        .UseInMemoryDatabase("ValidateRequiredProps");

    //  To disable the validation
    //  .UseInMemoryDatabase("ValidateRequiredProps", b => b.EnableNullChecks(false));
}

6EF.Functions.Contains 方法

在 EF Core 6.0 中，你可以使用 EF.Functions.Contains 方法來處理使用值轉(zhuǎn)換器映射的列（也可以處理二進(jìn)制列）。

using?var context = new ExampleContext();

var query = context.People
    .Where(e => EF.Functions.Contains(e.FullName, "Oleg"))
    .ToQueryString();

Console.WriteLine(query);
// SELECT[p].[Id], [p].[FullName]
// FROM[People] AS[p]
// WHERE CONTAINS([p].[FullName], N'Oleg')

class?Person
{
    public?int Id { get; set; }
    public FullName FullName { get; set; }
}
public?class?FullName
{
    public?string FirstName { get; set; }
    public?string LastName { get; set; }
}
class?ExampleContext : DbContext
{
    public?DbSet<Person> People { get; set; }

    protected?override?void?OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
            .Property(x => x.FullName)
            .HasConversion(
                v => JsonSerializer.Serialize(v, (JsonSerializerOptions)null),
                v => JsonSerializer.Deserialize(v, (JsonSerializerOptions)null));
    }

    protected?override?void?OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=EFCore6Contains");
}

7結(jié)尾

本文所有代碼示例都可以在我的 GitHub 中找到：

https://github.com/okyrylchuk/dotnet6_features/tree/main/EF%20Core%206#miscellaneous-enhancements

原文：bit.ly/3rlHxC9
作者：Oleg Kyrylchuk
翻譯：精致碼農(nóng)