.NET Core中如何使用Entity Framework操作PostgreSQL？

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我是靠谱客的博主糟糕御姐，这篇文章主要介绍.NET Core中如何使用Entity Framework操作PostgreSQL？，现在分享给大家，希望可以做个参考。

本篇文章给大家带来的内容是介绍.NET Core中使用Entity Framework操作PostgreSQL的方法。有一定的参考价值，有需要的朋友可以参考一下，希望对你们有所助。

Entity Framework在.NET Core中被命名为Entity Framework Core。虽然一般会用于对SQL Server数据库进行数据操作，但其实它还支持其它数据库，这里就以PostgreSQL作为例子。

PostgreSQL

PostgreSQL可以选用原生系统与Docker两种安装方式。

Official
Docker

Package

在应用程序工程中添加相关的引用。
dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL

Entity

编写两个实体类，用于映射User表与Order表。

复制代码public class User
{
    [Key]
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public virtual ICollection<Order> Orders { get; set; }

    public override string ToString()
    {
        var orders = new StringBuilder();
        foreach (var o in Orders)
        {
            orders.Append(o.ToString());
        }
        return $"UserId: {Id} Name: {Name} Orders: {orders.ToString()}";
    }
}1
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public class User
{
    [Key]
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public virtual ICollection<Order> Orders { get; set; }

    public override string ToString()
    {
        var orders = new StringBuilder();
        foreach (var o in Orders)
        {
            orders.Append(o.ToString());
        }
        return $"UserId: {Id} Name: {Name} Orders: {orders.ToString()}";
    }
}
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复制代码public class Order
{
    [Key]
    public int Id { get; set; }
    [Required]
    public int UserId { get; set; }
    [Required]
    public string Item { get; set; }
    [Required]
    public string Description { get; set; }
    public virtual User User { get; set; }

    public override string ToString()
    {
        return $"OrderId: {Id} Item: {Item} Descriptoin: {Description}";
    }
}1
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public class Order
{
    [Key]
    public int Id { get; set; }
    [Required]
    public int UserId { get; set; }
    [Required]
    public string Item { get; set; }
    [Required]
    public string Description { get; set; }
    public virtual User User { get; set; }

    public override string ToString()
    {
        return $"OrderId: {Id} Item: {Item} Descriptoin: {Description}";
    }
}
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DbContext

构建必要的DbContext类，并传入连接PostgreSQL所需的参数。

复制代码public class PurchaseDbContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Order> Orders { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder builder)
    {
        builder.UseNpgsql("Host=localhost;Username=postgres;Password=random;Database=Purchase");
    }
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public class PurchaseDbContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Order> Orders { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder builder)
    {
        builder.UseNpgsql("Host=localhost;Username=postgres;Password=random;Database=Purchase");
    }
}
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Seeder

构建一个用于初始化数据库的辅助类。

复制代码public class PurchaseDbContxtSeeder
{
    public static void Seed(PurchaseDbContext context)
    {
        context.Database.EnsureDeleted();
        context.Database.EnsureCreated();

        var users = new List<User>
            {
                new User { Name = "Tom" },
                new User { Name = "Mary" }
            };

        var orders = new List<Order>
            {
                new Order { User = users[0], Item = "cloth", Description = "handsome"},
                new Order {User = users[1], Item = "hat", Description = "red"},
                new Order {User = users[1], Item = "boot", Description = "black"}
            };

        context.Users.AddRange(users);
        context.Orders.AddRange(orders);

        context.SaveChanges();
    }
}1
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public class PurchaseDbContxtSeeder
{
    public static void Seed(PurchaseDbContext context)
    {
        context.Database.EnsureDeleted();
        context.Database.EnsureCreated();

        var users = new List<User>
            {
                new User { Name = "Tom" },
                new User { Name = "Mary" }
            };

        var orders = new List<Order>
            {
                new Order { User = users[0], Item = "cloth", Description = "handsome"},
                new Order {User = users[1], Item = "hat", Description = "red"},
                new Order {User = users[1], Item = "boot", Description = "black"}
            };

        context.Users.AddRange(users);
        context.Orders.AddRange(orders);

        context.SaveChanges();
    }
}
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Test

测试的程序第一步是调用生成数据的辅助类，第二步是查询数据表中的数据并在控制台中显示出来。

复制代码static void Main(string[] args)
{
    using (var context = new PurchaseDbContext())
    {
        PurchaseDbContxtSeeder.Seed(context);

        var users = context.Users.Include(u => u.Orders).ToList();
        users.ForEach(u =>
        {
            System.Console.WriteLine(u);
        });
    }
}1
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static void Main(string[] args)
{
    using (var context = new PurchaseDbContext())
    {
        PurchaseDbContxtSeeder.Seed(context);

        var users = context.Users.Include(u => u.Orders).ToList();
        users.ForEach(u =>
        {
            System.Console.WriteLine(u);
        });
    }
}
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