1.使用工具生成数据库对应的C# 类
添加包 EF Core design package NuGet Gallery | Home
使用用于 EF Core 迁移和现有数据库中的反向工程（基架）的工具需要安装相应的工具包：
- 可在 Visual Studio 包管理器控制台中使用的 PowerShell 工具的 Microsoft.EntityFrameworkCore.Tools
- 跨平台命令行工具的 dotnet-ef 和 Microsoft.EntityFrameworkCore.Design
请参阅 Entity Framework Core 工具参考，详细了解如何使用 EF Core 工具，包括如何在项目中或在全局范围内正确安装 dotnet-ef 工具。
2.生成的对应类库
2.1 数据库上下文类
using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;
#nullable disable
namespace Packt.Shared.AutoGen
{//DbContext 实例表示与数据库的会话，可用于查询和保存实体的实例。 DbContext 是工作单元和存储库模式的组合。
public partial class Northwind : DbContext
{
public Northwind()
{
}
public Northwind(DbContextOptions<Northwind> options)
: base(options)
{
}
public virtual DbSet<Category> Categories { get; set; } //数据集 类别
public virtual DbSet<Product> Products { get; set; }//数据集： 产品
/*
提供用于配置 Microsoft.EntityFrameworkCore.DbContextOptions 的简单 API 图面。
数据库（和其他扩展）通常在此对象上定义扩展方法，允许您配置要用于上下文的数据库连接（和其他选项）。
您可以使用 Microsoft.EntityFrameworkCore.DbContextOptionsBuilder 通过覆盖
Microsoft.EntityFrameworkCore.DbContext.OnConfiguring(Microsoft.EntityFrameworkCore.DbContextOptionsBuilder)
或在外部创建 Microsoft.EntityFrameworkCore.DbContextOptions 并将其传递给上下文构造函数来配置上下文。
*/
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{//为了保护连接字符串中的潜在敏感信息，您应该将其移出源代码。 您可以使用 Name= 语法从配置中读取连接字符串，从而避免构建连接字符串 - 请参阅 https://go.microsoft.com/fwlink/?linkid=2131148。 有关存储连接字符串的更多指导，请参阅 http://go.microsoft.com/fwlink/?LinkId=723263。
#warning To protect potentially sensitive information in your connection string, you should move it out of source code. You can avoid scaffolding the connection string by using the Name= syntax to read it from configuration - see https://go.microsoft.com/fwlink/?linkid=2131148. For more guidance on storing connection strings, see http://go.microsoft.com/fwlink/?LinkId=723263.
optionsBuilder.UseSqlite("Filename=Northwind.db");
}
}
//创建模型+
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Category>(entity =>
{
entity.Property(e => e.CategoryId)
.ValueGeneratedNever()
.HasColumnName("CategoryID");
entity.Property(e => e.CategoryName).HasAnnotation("Relational:ColumnType", "nvarchar (15)");
entity.Property(e => e.Description).HasAnnotation("Relational:ColumnType", "ntext");
entity.Property(e => e.Picture).HasAnnotation("Relational:ColumnType", "image");
});
modelBuilder.Entity<Product>(entity =>
{
entity.Property(e => e.ProductId)
.ValueGeneratedNever()
.HasColumnName("ProductID");
entity.Property(e => e.CategoryId)
.HasColumnName("CategoryID")
.HasAnnotation("Relational:ColumnType", "int");
entity.Property(e => e.Discontinued)
.HasDefaultValueSql("0")
.HasAnnotation("Relational:ColumnType", "bit");
entity.Property(e => e.ProductName).HasAnnotation("Relational:ColumnType", "nvarchar (40)");
entity.Property(e => e.QuantityPerUnit).HasAnnotation("Relational:ColumnType", "nvarchar (20)");
entity.Property(e => e.ReorderLevel)
.HasDefaultValueSql("0")
.HasAnnotation("Relational:ColumnType", "smallint");
entity.Property(e => e.SupplierId)
.HasColumnName("SupplierID")
.HasAnnotation("Relational:ColumnType", "int");
entity.Property(e => e.UnitPrice)
.HasDefaultValueSql("0")
.HasAnnotation("Relational:ColumnType", "money");
entity.Property(e => e.UnitsInStock)
.HasDefaultValueSql("0")
.HasAnnotation("Relational:ColumnType", "smallint");
entity.Property(e => e.UnitsOnOrder)
.HasDefaultValueSql("0")
.HasAnnotation("Relational:ColumnType", "smallint");
});
OnModelCreatingPartial(modelBuilder);
}
partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
}
}
2.2 类别类：
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;
#nullable disable
namespace Packt.Shared.AutoGen
{
[Index(nameof(CategoryName), Name = "CategoryName")]
public partial class Category
{
public Category()
{
Products = new HashSet<Product>();
}
[Key]
[Column("CategoryID")]
public long CategoryId { get; set; }
[Required]
[Column(TypeName = "nvarchar (15)")]
public string CategoryName { get; set; }
[Column(TypeName = "ntext")]
public string Description { get; set; }
[Column(TypeName = "image")]
public byte[] Picture { get; set; }
[InverseProperty(nameof(Product.Category))]
public virtual ICollection<Product> Products { get; set; }
}
}2.3 产品类
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;
#nullable disable
namespace Packt.Shared.AutoGen
{
[Index(nameof(CategoryId), Name = "CategoriesProducts")]
[Index(nameof(CategoryId), Name = "CategoryID")]
[Index(nameof(ProductName), Name = "ProductName")]
[Index(nameof(SupplierId), Name = "SupplierID")]
[Index(nameof(SupplierId), Name = "SuppliersProducts")]
public partial class Product
{
[Key]
[Column("ProductID")]
public long ProductId { get; set; }
[Required]
[Column(TypeName = "nvarchar (40)")]
public string ProductName { get; set; }
[Column("SupplierID", TypeName = "int")]
public long? SupplierId { get; set; }
[Column("CategoryID", TypeName = "int")]
public long? CategoryId { get; set; }
[Column(TypeName = "nvarchar (20)")]
public string QuantityPerUnit { get; set; }
[Column(TypeName = "money")]
public byte[] UnitPrice { get; set; }
[Column(TypeName = "smallint")]
public long? UnitsInStock { get; set; }
[Column(TypeName = "smallint")]
public long? UnitsOnOrder { get; set; }
[Column(TypeName = "smallint")]
public long? ReorderLevel { get; set; }
[Required]
[Column(TypeName = "bit")]
public byte[] Discontinued { get; set; }
[ForeignKey(nameof(CategoryId))]
[InverseProperty("Products")]
public virtual Category Category { get; set; }
}
}3. 数据库的操作
using static System.Console;
using Packt.Shared;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System.Collections.Generic;
using Microsoft.EntityFrameworkCore.Storage;
namespace WorkingWithEFCore
{
class Program
{ //查询类别
static void QueryingCategories()
{
using (var db = new Northwind())
{ //从实现 Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure`1 的类型公开的 System.IServiceProvider 解析服务。
// 此方法通常由数据库提供程序（和其他扩展）使用。 它通常不在应用程序代码中使用。
//Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure`1 用于隐藏不打算在应用程序代码中使用
//但可用于数据库提供程序编写的扩展方法等的属性。
var loggerFactory = db.GetService<ILoggerFactory>();
loggerFactory.AddProvider(new ConsoleLoggerProvider());//将 Microsoft.Extensions.Logging.ILoggerProvider 添加到日志系统。
WriteLine("Categories and how many products they have:");
// a query to get all categories and their related products
IQueryable<Category> cats;//获取所有类别及其相关产品的查询
// = db.Categories;
// .Include(c => c.Products);
//获取或设置一个值，该值指示是否将在首次访问时加载被跟踪实体的导航属性。
// 默认值是true。 但是，延迟加载只会发生在实体的导航属性中，这些实体也已在模型中配置为延迟加载。
db.ChangeTracker.LazyLoadingEnabled = false;//默认true
Write("Enable eager loading? (Y/N): ");//启用预加载
bool eagerloading = (ReadKey().Key == ConsoleKey.Y);
bool explicitloading = false;
WriteLine();
if (eagerloading)//预加载 产品数量非零
{
cats = db.Categories.Include(c => c.Products);//指定要包含在查询结果中的相关实体。 要包含的导航属性从被查询实体的类型 (TEntity) 开始指定。
}
else
{
cats = db.Categories;
Write("Enable explicit loading? (Y/N): ");//Y 显式加载 产品数量非零
explicitloading = (ReadKey().Key == ConsoleKey.Y);
WriteLine();
}
foreach (Category c in cats)
{
if (explicitloading)//显式加载每个类别
{
Write($"Explicitly load products for {c.CategoryName}? (Y/N): "); //Y 产品数量输出非零
ConsoleKeyInfo key = ReadKey();
WriteLine();
if (key.Key == ConsoleKey.Y)
{
var products = db.Entry(c).Collection(c2 => c2.Products);//获取类别c的 产品型号集合
if (!products.IsLoaded) products.Load();
}
}
WriteLine($"{c.CategoryName} has {c.Products.Count} products.");
}
}
}
//过滤器查询 各类
// 对应的各种产品中，库存量大于stock的产品有哪些？
static void FilteredIncludes()
{
using (var db = new Northwind())
{
Write("Enter a minimum for units in stock: ");
string unitsInStock = ReadLine();
int stock = int.Parse(unitsInStock);//库存单位
//查找 库存量大于stock的产品类别
IQueryable<Category> cats = db.Categories
.Include(c => c.Products.Where(p => p.Stock >= stock));//要求该类的产品种类中数量大于stock
WriteLine($"ToQueryString: {cats.ToQueryString()}");
foreach (Category c in cats)
{ //某类 库存大于stock的产品有哪些
WriteLine($"{c.CategoryName} has {c.Products.Count} products with a minimum of {stock} units in stock.");
foreach (Product p in c.Products)
{
WriteLine($" {p.ProductName} has {p.Stock} units in stock.");//输出产品名 产品库存
}
}
}
}
//查询产品
static void QueryingProducts()
{
using (var db = new Northwind())
{
var loggerFactory = db.GetService<ILoggerFactory>();
loggerFactory.AddProvider(new ConsoleLoggerProvider());
WriteLine("Products that cost more than a price, highest at top.");
string input;
decimal price; //价格
do
{
Write("Enter a product price: ");
input = ReadLine();
} while (!decimal.TryParse(input, out price));//输入产品价格
IQueryable<Product> prods = db.Products
.Where(product => product.Cost > price) //产品单价大于price
.OrderByDescending(product => product.Cost); //按照 产品单价 降序排列
/*
// alternative "fix"
IOrderedEnumerable<Product> prods = db.Products
.AsEnumerable() // force client-side execution
.Where(product => product.Cost > price)
.OrderByDescending(product => product.Cost);
*/
foreach (Product item in prods)
{//38: C?te de Blaye costs $263.50 and has 17 in stock.
WriteLine(
"{0}: {1} costs {2:$#,##0.00} and has {3} in stock.",
item.ProductID, item.ProductName, item.Cost, item.Stock);
}
}
}
//like查询
static void QueryingWithLike()
{
using (var db = new Northwind())
{
var loggerFactory = db.GetService<ILoggerFactory>();
loggerFactory.AddProvider(new ConsoleLoggerProvider());
Write("Enter part of a product name: ");
string input = ReadLine();
IQueryable<Product> prods = db.Products
.Where(p => EF.Functions.Like(p.ProductName, $"%{input}%"));//包含 {input} 的 产品名
foreach (Product item in prods)
{
WriteLine("{0} has {1} units in stock. Discontinued? {2}",
item.ProductName, item.Stock, item.Discontinued);
}
}
}
//添加产品
static bool AddProduct(int categoryID, string productName, decimal? price)
{
using (var db = new Northwind())
{
var newProduct = new Product
{
CategoryID = categoryID,//类别id 产品id自增加
ProductName = productName,
Cost = price
};
// mark product as added in change tracking
db.Products.Add(newProduct);
// save tracked changes to database
int affected = db.SaveChanges();//将跟踪的更改保存到数据库
return (affected == 1);
}
}
//列出产品
static void ListProducts()
{
using (var db = new Northwind())
{
WriteLine("{0,-3} {1,-35} {2,8} {3,5} {4}",
"ID", "Product Name", "Cost", "Stock", "Disc.");
foreach (var item in db.Products.OrderByDescending(p => p.Cost))
{
WriteLine("{0:000} {1,-35} {2,8:$#,##0.00} {3,5} {4}",
item.ProductID, item.ProductName, item.Cost,
item.Stock, item.Discontinued);
}
}
}
//增加产品价格
static bool IncreaseProductPrice(string name, decimal amount)
{
using (var db = new Northwind())
{
// get first product whose name starts with name
Product updateProduct = db.Products.First(
p => p.ProductName.StartsWith(name));
updateProduct.Cost += amount;
int affected = db.SaveChanges();
return (affected == 1);
}
}
//删除产品
static int DeleteProducts(string name)
{
using (var db = new Northwind())
{
using (IDbContextTransaction t = db.Database.BeginTransaction())//开始一个新的事务。
{
WriteLine("Transaction isolation level: {0}",
t.GetDbTransaction().IsolationLevel);
var products = db.Products.Where(
p => p.ProductName.StartsWith(name));
db.Products.RemoveRange(products);
int affected = db.SaveChanges();
t.Commit();
return affected;
}
}
}
static void Main(string[] args)
{
// QueryingCategories();
// FilteredIncludes();
//QueryingProducts();
//QueryingWithLike();
//if (AddProduct(6, "Bob's Burgers", 500M))
//{
// WriteLine("Add product successful.");
//}
//if (IncreaseProductPrice("Bob", 20M))
//{
// WriteLine("Update product price successful.");
//}
int deleted = DeleteProducts("Bob");
WriteLine($"{deleted} product(s) were deleted.");
// ListProducts();
ReadLine();
}
}
}4. Loggin EF Core
using Microsoft.Extensions.Logging;
using System;
using static System.Console;
namespace Packt.Shared
{
public class ConsoleLoggerProvider : ILoggerProvider//创建日志提供器
{
public ILogger CreateLogger(string categoryName)
{
return new ConsoleLogger();//控制台记录器
}
// if your logger uses unmanaged resources,
// you can release the memory here 如果您的记录器使用非托管资源，您可以在此处释放内存
public void Dispose() { }
}
public class ConsoleLogger : ILogger //日志记录器
{
// if your logger uses unmanaged resources, you can
// return the class that implements IDisposable here
//如果您的记录器使用非托管资源，您可以在此处返回实现 IDisposable 的类
public IDisposable BeginScope<TState>(TState state)
{
return null;
}
//为避免过度记录，您可以在日志级别上进行过滤
public bool IsEnabled(LogLevel logLevel)
{
// to avoid overlogging, you can filter
// on the log level 为避免过度记录，您可以在日志级别上进行过滤
switch (logLevel)
{
case LogLevel.Trace:
case LogLevel.Information:
case LogLevel.None:
return false;
case LogLevel.Debug:
case LogLevel.Warning:
case LogLevel.Error:
case LogLevel.Critical:
default:
return true;
};
}
//记录日志
public void Log<TState>(LogLevel logLevel,
EventId eventId, TState state, Exception exception,
Func<TState, Exception, string> formatter)
{
if (eventId.Id == 20100)
{
// 记录级别和事件标识符 log the level and event identifier
Write($"Level: {logLevel}, Event ID: {eventId.Id}");
//仅在存在时输出状态或异常 only output the state or exception if it exists
if (state != null)
{
Write($", State: {state}");
}
if (exception != null)
{
Write($", Exception: {exception.Message}");
}
WriteLine();
}
}
}
}5. 设置sqlite for windows
| sqlite-tools-win32-x86-3410200.zip (1.91 MiB) |
A bundle of command-line tools for managing SQLite database files, including the command-line shell program, the sqldiff.exe program, and the sqlite3_analyzer.exe program. (SHA3-256: 0ceebb7f8378707d6d6b0737ecdf2ba02253a3b44b1009400f86273719d98f1f) |
解压并设置环境变量（exe 所在目录添加到path）