C#

public Response UpdateRuleDefinition(RuleDefintionEntity entity)
{
    var response = new Response();

    try
    {
        IRulesBL bl = GetBL();
        bl.UpdateRuleDefinition(entity);
    }
    catch (Exception e)
    {
        response.Exception = e;
    }

    return response;
}
private IRulesBL GetBL()
{
    return new RulesBL(ConnectionString, DatabaseName);
}

public class APIControllerBase : ApiController
{
    public string ConnectionString { get; private set; }

    public string DatabaseName { get; private set; }

    public APIControllerBase()
    {
        ConnectionString = Properties.Settings.Default.ConnectionString;
        DatabaseName = Properties.Settings.Default.DatabaseName;
    }

    // This is what I want to add
    public T GetBL<T>() where T : new()
    {
        return new T();
    }

The class I use in the project is a SQLite database that helps static classes. It can be called directly without using instantiation.
Originally there are a lot of related classes on the Internet. After using a class, you can't call it.

private void TextBox2_TextChanged(object sender, EventArgs e)  //新增插入数据
          {
             SQLiteCommand cmdInsert = new SQLiteCommand(mConn);
            string sql = "INSERT INTO KD(postID,ddtime)values(@postID,@ddtime)";
            SQLiteParameter[] cmdParms = new SQLiteParameter[]{
             new SQLiteParameter("@postID", (textBox2.Text)),
             new SQLiteParameter("@ddtime", DateTime.Now)
                   };
            cmd.ExecuteNonQuery(sql,cmdParms);
}

The SQLiteHelper class source is as follows

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Data.SQLite;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace SQLiteQueryBrowser
{
    /// <summary>
    /// 本类为SQLite数据库帮助静态类,使用时只需直接调用即可,无需实例化
    /// </summary>
    public static class SQLiteHelper
    {
        /// <summary>
        /// 数据库连接字符串
        /// </summary>
        //public static string connectionString = "Data Source=" + Application.StartupPath + "\\" + System.Configuration.ConfigurationSettings.AppSettings["Contr"];
        public static string connectionString = "Data Source=" + Application.StartupPath + "/KDDB.db";

        #region 执行数据库操作(新增、更新或删除)，返回影响行数
        /// <summary>
        /// 执行数据库操作(新增、更新或删除)
        /// </summary>
        /// <param name="cmd">SqlCommand对象</param>
        /// <returns>所受影响的行数</returns>
        public static int ExecuteNonQuery(SQLiteCommand cmd)
        {
            int result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, cmd.CommandType, cmd.CommandText);
                try
                {
                    result = cmd.ExecuteNonQuery();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }

        /// <summary>
        /// 执行数据库操作(新增、更新或删除)
        /// </summary>
        /// <param name="commandText">执行语句或存储过程名</param>
        /// <param name="commandType">执行类型(默认语句)</param>
        /// <returns>所受影响的行数</returns>
        public static int ExecuteNonQuery(string commandText, CommandType commandType = CommandType.Text)
        {
            int result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            if (commandText == null || commandText.Length == 0)
                throw new ArgumentNullException("commandText");
            SQLiteCommand cmd = new SQLiteCommand();
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, commandType, commandText);
                try
                {
                    result = cmd.ExecuteNonQuery();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }

        /// <summary>
        /// 执行数据库操作(新增、更新或删除)
        /// </summary>
        /// <param name="commandText">执行语句或存储过程名</param>
        /// <param name="commandType">执行类型(默认语句)</param>
        /// <param name="cmdParms">SQL参数对象</param>
        /// <returns>所受影响的行数</returns>
        public static int ExecuteNonQuery(string commandText, CommandType commandType = CommandType.Text, params SQLiteParameter[] cmdParms)
        {
            int result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            if (commandText == null || commandText.Length == 0)
                throw new ArgumentNullException("commandText");

            SQLiteCommand cmd = new SQLiteCommand();
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, commandType, commandText, cmdParms);
                try
                {
                    result = cmd.ExecuteNonQuery();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }
        #endregion

        #region 执行数据库操作(新增、更新或删除)同时返回执行后查询所得的第1行第1列数据
        /// <summary>
        /// 执行数据库操作(新增、更新或删除)同时返回执行后查询所得的第1行第1列数据
        /// </summary>
        /// <param name="cmd">SqlCommand对象</param>
        /// <returns>查询所得的第1行第1列数据</returns>
        public static object ExecuteScalar(SQLiteCommand cmd)
        {
            object result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, cmd.CommandType, cmd.CommandText);
                try
                {
                    result = cmd.ExecuteScalar();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }

        /// <summary>
        /// 执行数据库操作(新增、更新或删除)同时返回执行后查询所得的第1行第1列数据
        /// </summary>
        /// <param name="commandText">执行语句或存储过程名</param>
        /// <param name="commandType">执行类型（默认语句）</param>
        /// <returns>查询所得的第1行第1列数据</returns>
        public static object ExecuteScalar(string commandText, CommandType commandType = CommandType.Text)
        {
            object result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            if (commandText == null || commandText.Length == 0)
                throw new ArgumentNullException("commandText");
            SQLiteCommand cmd = new SQLiteCommand();
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, commandType, commandText);
                try
                {
                    result = cmd.ExecuteScalar();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }

        /// <summary>
        /// 执行数据库操作(新增、更新或删除)同时返回执行后查询所得的第1行第1列数据
        /// </summary>
        /// <param name="commandText">执行语句或存储过程名</param>
        /// <param name="commandType">执行类型(默认语句)</param>
        /// <param name="cmdParms">SQL参数对象</param>
        /// <returns>查询所得的第1行第1列数据</returns>
        public static object ExecuteScalar(string commandText, CommandType commandType = CommandType.Text, params SQLiteParameter[] cmdParms)
        {
            object result = 0;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");
            if (commandText == null || commandText.Length == 0)
                throw new ArgumentNullException("commandText");

            SQLiteCommand cmd = new SQLiteCommand();
            using (SQLiteConnection con = new SQLiteConnection(connectionString))
            {
                SQLiteTransaction trans = null;
                PrepareCommand(cmd, con, ref trans, true, commandType, commandText, cmdParms);
                try
                {
                    result = cmd.ExecuteScalar();
                    trans.Commit();
                }
                catch (Exception ex)
                {
                    trans.Rollback();
                    throw ex;
                }
            }
            return result;
        }
        #endregion

        #region 执行数据库查询，返回SqlDataReader对象
        /// <summary>
        /// 执行数据库查询，返回SqlDataReader对象
        /// </summary>
        /// <param name="cmd">SqlCommand对象</param>
        /// <returns>SqlDataReader对象</returns>
        public static DbDataReader ExecuteReader(SQLiteCommand cmd)
        {
            DbDataReader reader = null;
            if (connectionString == null || connectionString.Length == 0)
                throw new ArgumentNullException("connectionString");

            SQLiteConnection con = new SQLiteConnection(connectionString);
            SQLiteTransaction trans = null;
            PrepareCommand(cmd, con, ref trans, false, cmd.CommandType, cmd.CommandText);
            try
            {
                reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch (Exception ex)
            {
                throw ex;
            }
            return reader;
        }

        /// <summary>
        /// 执行数据库查询，返回SqlDataReader对象
        /// </summary>
        /// <param name="commandText">执行语句或存储过程名</param>
        /// <param name="commandType">执行类型(默认语句)</param>
        /// <returns>Sql

Public Shared Function GetSettings() As RootObject

            Dim oRootObject As RootObject = Nothing
            Dim appData = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)
            Dim appPath = appData + My.Resources.AppSettingsJsonPath
            If Not (File.Exists(appPath)) Then
                Create_AppSettings()
            End If

            Try

                Using jsonStream = New FileStream(appPath, FileMode.Open, FileAccess.Read)

                    Dim fileLen = jsonStream.Length
                    Dim fileData = New Byte(fileLen) {}
                    Dim jsonLen = jsonStream.Read(fileData, 0, fileLen)
                    Dim fileText = Encoding.UTF8.GetString(fileData)
                    oRootObject = JsonConvert.DeserializeObject(Of RootObject)(fileText)

                End Using

            Catch ex As Exception
                ErrorLogging.NLog_Exception(ex, "Read appSettings.json")
            End Try

            Return oRootObject

        End Function

Public Shared Sub WriteSettings(ByVal rootObject As RootObject)

            Dim appData = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)
            Dim appPath = appData + My.Resources.AppSettingsJsonPath
            If Not (IsFileInUse(appPath)) Then

                If rootObject.ProductInfo IsNot Nothing Then
                    rootObject.ProductInfo.Name = Application.ProductName
                    rootObject.ProductInfo.Version = Application.ProductVersion
                End If

                If rootObject.Settings IsNot Nothing Then
                    rootObject.Settings.Version = Application.ProductVersion
                End If

                Try

                    Dim oJs = JsonConvert.SerializeObject(rootObject, Formatting.Indented)
                    Do Until Not IsFileInUse(appPath)
                        Application.DoEvents()
                    Loop
                    Dim bytes() = New UTF8Encoding(True).GetBytes(oJs)
                    Using jsonStream = File.OpenWrite(appPath)
                        jsonStream.Write(bytes, 0, bytes.Length)
                    End Using

                Catch ex As Exception
                    ErrorLogging.NLog_Exception(ex, "Write appSettings.json")
                End Try

            End If

        End Sub