BuecherwurmAPI/Models/LendModel.cs

using System;
using System.Collections.Generic;
using BuecherwurmAPI.Models;
using Microsoft.Data.Sqlite;
using Microsoft.VisualBasic.CompilerServices;

namespace BuecherwurmAPI.Models
{

    public interface ILend
    {
        
    }

    internal class LendModel : ILend
    {
        private SqliteConnection _dbConnection;
        
        public LendModel()
        {
            var connectionBuilder = new SqliteConnectionStringBuilder {DataSource = "LongWormMemory.db"};
            _dbConnection = new SqliteConnection(connectionBuilder.ConnectionString);
            _dbConnection.Open();
        }

        public bool IdExits(string table, long id)
        {
            using (var command = _dbConnection.CreateCommand())
            {
                command.Parameters.Add(new SqliteParameter("@Id", SqliteType.Integer)).Value = id;
                
                // Certain parts of the query can't be filled with variables for security reasons.
                switch (table)
                {
                    case Tables.Table.Lends: 
                        command.CommandText = @"SELECT EXISTS(SELECT 0 FROM Lends WHERE Id = @Id)";
                        break;
                }
                
                var dr = command.ExecuteReader();
                
                long result = 0;
                while (dr.Read())
                {
                    result = (long) dr[0];
                }
                return result != 0;
            }
        }

        public IEnumerable<Lend> GetAllLends()
        {
            var lends = new List<Lend>();

            // using automatically disposes the command after completion
            using (var command = _dbConnection.CreateCommand())
            {
                command.CommandText = @"SELECT * FROM Lends";
                var dataReader = command.ExecuteReader();
                
                while (dataReader.Read())
                {
                    var returned = (long) dataReader["Returned"] == 1;
                    
                    lends.Add(new Lend
                    {
                        Id = (long) dataReader["Id"],
                        Customer = (string) dataReader["Customer"],
                        ItemId = (long) dataReader["ItemId"],
                        Returned = returned,
                        ReturnDate = DateTime.Parse((string)dataReader["ReturnDate"])
                    });
                }
            }
            return lends;
        }

        public Lend GetLendById(long id)
        {
            using (var command = _dbConnection.CreateCommand())
            {
                command.Parameters.Add(new SqliteParameter("@id", SqliteType.Integer)).Value = id;
                command.CommandText = @"SELECT * FROM Lends WHERE Id = @id";
                var dataReader = command.ExecuteReader();

                while (dataReader.Read())
                {
                    var returned = (long) dataReader["Returned"] == 1;

                    var lend = new Lend
                    {
                        Id = (long) dataReader["Id"],
                        Customer = (string) dataReader["Customer"],
                        ItemId = (long) dataReader["ItemId"],
                        Returned = returned,
                        ReturnDate = DateTime.Parse((string) dataReader["ReturnDate"])
                    };
                    return lend;
                }
            }
            return null;
        }

        public long insertLendReturningId(LendPost lend)
        {
            using (var command = _dbConnection.CreateCommand())
            {
                command.CommandText = "INSERT INTO Lends VALUES (NULL, @itemId, @returnDate, @customer, false)";
                command.Parameters.Add(new SqliteParameter("@itemId", lend.ItemId));
                command.Parameters.Add(new SqliteParameter("@returnDate", lend.ReturnDate));
                command.Parameters.Add(new SqliteParameter("@customer", lend.Customer));

                var success = command.ExecuteNonQuery();

                if (success == 1)
                {
                    command.CommandText = @"SELECT last_insert_rowid()";
                    return (long)command.ExecuteScalar();
                }

                return -1;
            }
        }
    }
}