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125 lines
2.8 KiB
Markdown
125 lines
2.8 KiB
Markdown
# Entity Framework
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## Model & Data Annotations
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```cs
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using System;
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using System.Collections.Generic;
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using System.ComponentModel.DataAnnotations;
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using System.Linq;
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namespace <Project>.Model
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{
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public class Entity
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{
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[Key] // set as PK (Id & EntityId are automatically detected to be PKs)
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public int Id { get; set; }
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[Required]
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public Type ForeignObject { get; set; } // Not Null in DB
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public Type ForeignObject { get; set; } // Allow Null in DB
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public int Prop { get; set; } // Not Null in DB (primitive are not nullable)
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public int? Prop { get; set; } // Allow Null in DB
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}
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}
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```
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## Context
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NuGet Packages to install:
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- `Microsoft.EntityFrameworkCore`
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- `Microsoft.EntityFrameworkCore.Tools` to use migrations in Visual Studio
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- `Microsoft.EntityFrameworkCore.Tools.DotNet` to use migrations in `dotnet` cli (`dotnet-ef`)
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- `Microsoft.EntityFrameworkCore.Design` *or* `Microsoft.EntityFrameworkCore.<db_provider>.Design` needed for tools to work (bundled w\ tools)
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- `Microsoft.EntityFrameworkCore.<db_provider>`
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```cs
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using Microsoft.EntityFrameworkCore;
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namespace <Project>.Model
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{
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class Context : DbContext
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{
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private const string _connectionString = "Server=<server_name>;Database=<database>;UID=<user>;Pwd=<password>";
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// connect to db
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protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
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{
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optionsBuilder.UseSqlServer(_connectionString); // specify connection
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}
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// or
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public Context(DbContextOptions options) : base(options)
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{
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}
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//DBSet<TEntity> represents the collection of all entities in the context (or that can be queried from the database) of a given type
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public DbSet<Entity> Entities { get; set; }
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public DbSet<Entity> Entities => Set<Entity>(); // with nullable reference types
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}
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}
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```
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## Migrations
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Create & Update DB Schema if necessary.
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In Package Manager Shell:
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```ps1
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PM> Add-Migration <migration_name>
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PM> update-database [-Verbose] # use the migrations to modify the db, -Verbose to show SQL queries
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```
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In dotnet cli:
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```ps1
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dotnet tool install --global dotnet-ef # if not already installed
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dotnet ef migrations add <migration_name>
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dotnet ef database update
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```
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## CRUD
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### Create
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```cs
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context.Add(entity);
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context.AddRange(entities);
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context.SaveChanges();
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```
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### Read
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[Referenced Object Not Loading Fix](https://stackoverflow.com/a/5385288)
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```cs
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context.Entities.ToList();
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context.Entities.Find(id);
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// force read of foreign key identifying referenced obj
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context.Entities.Include(c => c.ForeignObject).Find(id);
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```
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### Update
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```cs
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context.Entities.Update(entity);
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context.UpdateRange(entities);
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context.SaveChanges();
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```
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### Delete
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```cs
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context.Entities.Remove(entity);
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context.RemoveRange(entities);
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context.SaveChanges();
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```
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