Rename .NET folder to DotNet

DotNet/Database/EntityFramework.md

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