EF 6 新特性八

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-3

正文

SQLite 中的保存点

在 EF Core 6.0 中，SQLite 支持保存点。您可以保存、回滚和释放保存点。

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();

内存数据库验证所需属性

在 EF Core 6.0 中，内存数据库验证所需的属性。如果您尝试为所需属性保存具有空值的实体，则会引发异常。如有必要，您可以禁用此验证。

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<Blog> 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));
}

EF.Functions.Contains 带值转换器

您可以将EF.Functions.Contains方法与使用 EF Core 6.0 中的值转换器（也与二进制列）映射的列一起使用。

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<Person>()
            .Property(x => x.FullName)
            .HasConversion(
                    v => JsonSerializer.Serialize(v, (JsonSerializerOptions)null),
                    v => JsonSerializer.Deserialize<FullName>(v, (JsonSerializerOptions)null));
    }

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

结语

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