在这篇文章中，你将看到 EF Core 对 SQLite、In-memory 提供者和 EF.Functions.Contains 方法的改进。
这是 EF Core 6 新功能汇总的第四篇文章：
1 SQLite 支持 DateOnly 和 TimeOnly
在 EF Core 6.0 中，SQLite 提供者支持新的 DateOnly 和 TimeOnly 类型。它将它们存储为 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<Person> People { get; set; }
public DbSet<Notification> Notifications { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder options)
=> options.UseSqlite(@"Data Source=Db\DateOnlyTimeOnly.db");
}
2 SQLite 连接是池化的
SQLite 数据库是一个文件。因此，在大多数情况下，创建一个连接是很快的。然而，打开一个加密数据库的连接会非常慢。因此，在 EF Core 6 中，SQLite 连接现在是池化的，就像其他数据库提供者一样。
class Person
{
public int Id { get; set; }
public string Name { get; set; }
}
class ExampleContext : DbContext
{
public DbSet<Person> People { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder options)
=> options.UseSqlite("Data Source=EncryptedDb.db;Mode=ReadWriteCreate;Password=password");
}
3 SQLite 中的命令超时
在 EF Core 6 的 SQLite 中，支持添加 Command Timeout 命令到连接字符串中，你可以用它来指定 SQLite 的默认超时时间。
class Person
{
public int Id { get; set; }
public string Name { get; set; }
}
class ExampleContext : DbContext
{
public DbSet<Person> 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");
}
4 SQLite 中的保存点
在 EF Core 6.0 中，SQLite 支持保存点(Savepoints)。你可以保存、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();
5 内存数据库验证必需属性
在 EF Core 6.0 中，内存(In-memory)数据库验证了必需（In-momory）的属性。如果你试图保存一个实体的必需属性值为空，就会出现异常。如果有必要，你可以禁用这个验证。
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));
}
6 EF.Functions.Contains 方法
在 EF Core 6.0 中，你可以使用 EF.Functions.Contains 方法来处理使用值转换器映射的列（也可以处理二进制列）。
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<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");
}
7 结尾
本文所有代码示例都可以在我的 GitHub 中找到：https://github.com/okyrylchuk/dotnet6_features/tree/main/EF%20Core%206#miscellaneous-enhancements
原文：https://blog.okyrylchuk.dev/entity-framework-core-6-features-part-3
作者：Oleg Kyrylchuk
翻译：精致码农
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