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.NET/Database/ADO.NET.md

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+# [ADO.NET](https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/ "ADO.NET Docs")
+
+`ADO.NET` is a set of classes that expose data access services for .NET.
+The `ADO.NET` classes are found in `System.Data.dll`, and are integrated with the XML classes found in `System.Xml.dll`.
+
+[ADO.NET provider for SQLite](https://system.data.sqlite.org/index.html/doc/trunk/www/index.wiki "System.Data.SQLite")
+
+## [Connection Strings](https://www.connectionstrings.com)
+
+### [SQL Server 2019](https://www.connectionstrings.com/sql-server-2019/)
+
+- Standard Security:
+  - `Server=<server_name>; Database=<database>; UID=<user>; Pwd=<password>;`
+  - `Server=<server_name>; Database=<database>; User ID=<user>; Password=<password>;`
+  - `Data Source=<server_name>; Initial Catalog=<database>; UID=<user>; Pwd=<password>;`
+- Specific Instance: `Server=<server_name>\<instance_name>; Database=<database>; User ID=<user>; Password=<password>;`
+- Trusted Connection (WinAuth): `Server=<server_name>; Database=<database>; Trusted_Connection=True;`
+- MARS: `Server=<server_name>; Database=<database>; Trusted_Connection=True; MultipleActiveResultSets=True;`
+
+**NOTE**: *Multiple Active Result Sets* (MARS) is a feature that works with SQL Server to allow the execution of multiple batches on a single connection.
+
+### [SQLite](https://www.connectionstrings.com/sqlite/)
+
+- Basic: `Data Source: path\to\db.sqlite3; Version=3;`
+- In-Memory Dataabse: `Data Source=:memory:; Version=3; New=True`
+- With Password: `Data Source: path\to\db.sqlite3; Version=3; Password=<password>`
+
+## Connection to DB
+
+```cs
+using System;
+using System.Data.SqlClient;  // ADO.NET Provider, installed through NuGet
+
+namespace <namespace>
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            // Connection to SQL Server DBMS
+            SqlConnectionStringBuilder connectionString = new SqlConnectionStringBuilder();
+            connectionString.DataSource = "<server_name>";
+            connectionString.UserID = "<user>";
+            connectionString.Password = "<password>";
+            connectionString.InitialCatalog = "<database>";
+
+            // more compact
+            SqlConnectionStringBuilder connectionString = new SqlConnectionStringBuilder("Server=<server_name>;Database=<database>;UID=<user>;Pwd=<password>")
+        }
+    }
+}
+```
+
+## DB Interrogation
+
+### `SqlConnection`
+
+```cs
+using (SqlConnection connection = new SqlConnection())
+{
+    connection.ConnectionString = connectionString.ConnectionString;
+    connection.Open();  // start comunication w/ sql server
+}
+
+// more compact
+using (SqlConnection connection = new SqlConnection(connectionString)) {
+    connection.Open()
+}
+```
+
+### [SqlCommand](https://docs.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlcommand)
+
+```cs
+string sql = "<sql_instruction>";
+
+using (SqlCommand command = new SqlCommand())
+{
+    command.Connection = connection;  // SqlConnection
+    command.CommandText = "... @Parameter";  // or name of StoredProcedure
+
+    // add parameters to the SqlParameterCollection, WARNING: table names or columns cannot be parameters
+    command.Parameters.Add("@Parameter", SqlDbType.<DBType>, columnLength).Value = value;
+    command.Parameters.AddWithValue("@Parameter", value);
+    command.Parameters.AddWithValue("@Parameter", (object) value ?? DBNull.Value);  // if Parameter is nullable
+
+    // Create an instance of a SqlParameter object.
+    command.CreateParameter();
+
+    command.CommandType = CommandType.Text;  // or StoredProcedure
+
+    int affectedRows = command.ExecuteNonQuery();  // execute the query and return the number of affected rows
+}
+```
+
+### `SqlDataReader`
+
+```cs
+using (SqlDataReader cursor = command.ExecuteReader())  // object to get data from db
+{
+    while (cursor.Read())  // get data till possible
+    {
+        // preferred methodology
+        cursor["<column_name>"].ToString();  // retrieve data form the column
+        cursor[<column_index>].ToString();  // retrieve data form the column
+
+        // check for null before retrieving the value
+        if(!cursor.IsDBNull(n))
+        {
+            sqlreader.Get<SystemType>(index);  // retrieve data form the n-th column
+        }
+    }
+}
+```

.NET/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
+- `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
+    {
+        public Context(DbContextOptions options) : base(options)
+        {
+        }
+    }
+
+    // or
+
+    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
+        }
+
+        //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; }
+    }
+}
+```
+
+## 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
+public static bool InsertOne(Entity entity)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.Add(entity);
+        context.SaveChanges();
+    }
+
+    return rows == 1;
+}
+
+public static bool InsertMany(IEnumerable<Entity> entities)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.AddRange(entities);
+        context.SaveChanges();
+    }
+
+    return rows == entities.Count();
+}
+```
+
+### Read
+
+[Referenced Object Not Loading Fix](https://stackoverflow.com/a/5385288)
+
+```cs
+public static List<Entity> SelectAll()
+{
+    using(var context = new Context())
+    {
+        return context.Entities.ToList();
+    }
+}
+
+static Entity SelectOneById(int id)
+{
+    using(var context = new Context())
+    {
+        return context.Entities.Find(id);
+
+        // force read of foreign key identifying referenced obj
+        return context.Entities.Include(c => c.ForeignObject).Find(id);
+
+    }
+}
+```
+
+### Update
+
+```cs
+public static bool UpdateOne(Entity entity)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.Entities.Update(entity);
+        context.SaveChanges();
+    }
+
+    return rows == 1;
+}
+
+public static bool UpdateMany(IEnumerable<Entity> entities)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.UpdateRange(entities);
+        context.SaveChanges();
+    }
+
+    return rows == entities.Count();
+}
+```
+
+### Delete
+
+```cs
+public static bool DeleteOne(Entity entity)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.Entities.Remove(entity);
+        context.SaveChanges();
+    }
+
+    return rows == 1;
+}
+
+public static bool DeleteMany(IEnumerable<Entity> entities)
+{
+    int rows = 0;
+
+    using(var context = new Context())
+    {
+        context.RemoveRange(entities);
+        context.SaveChanges();
+    }
+
+    return rows == entities.Count();
+}
+```