c#-检查数据库中的重复值

在将TextBox中的值保存到数据库中之前,我需要检查该值是否已存在于数据库中.

这是TextBox代码：

 <tr>
        <td>
            <asp:Label ID="lblProductConstruction" runat="server" Text="Product Construction:" Font-Names="Open Sans"></asp:Label></td>
        <td>
            <asp:TextBox ID="txtProductConstruction" runat="server"  Font-Names="Merriweather" margin-Left="100px" ></asp:TextBox><br />
        </td>
    </tr>
    <tr>

保存按钮：

<input type="button" class="button" id="myButton" value="Save"/>

在按钮上单击Ajax：

 $(function () {

             $('#myButton').on('click', function () {

                 var lvl = $('#MainContent_txtProductConstruction').val()

                 $.ajax({
                     type: "POST",
                     url: "NewProductConstruction.aspx/GetCollection",

                     data: JSON.stringify({'lvl': lvl }),

                     contentType: "application/json; charset=utf-8",
                     dataType: "json",

                     success: function (response) {
                         alert("Saved successfully.");
                         console.log(response);
                         location.reload(true);

                     },
                     error: function (response) {
                         alert("Not Saved!");
                         console.log(response);
                         location.reload(true);
                     }

                 });

             });

         });

WebMethod接收值并将该参数(@LvlName)发送到数据库：

[WebMethod(EnableSession = true)]
        public static void GetCollection(string lvl)
        {

            //string strMsg = "";
            string conn = ConfigurationManager.ConnectionStrings["Connection"].ConnectionString;
            using (sqlConnection connection = new sqlConnection(conn))
                try
                {
                    connection.open();
                    sqlCommand cmdProc = new sqlCommand("InsertLvlName", connection);
                    cmdProc.CommandType = CommandType.StoredProcedure;
                    cmdProc.Parameters.AddWithValue("@LvlName", lvl);
                    cmdProc.ExecuteNonQuery();
                    //strMsg = "Saved successfully.";

                }
                catch
                {

                }
                finally
                {
                    connection.Close();

                }

            return;

        }

我需要帮助检查两件事：
1)要查看文本框是否为空,如果是这种情况,请不要将该值保存到数据库中,并显示警报此字段需要某种值.

2)我需要某种检查,如果数据库中已经存在相同字段的值,则不要保存它.

提前致谢 ！

解决方法:

这是我们可以使用jquery进行的简单验证

if (inp.val().length > 0) {
    //do something
}
else
{
alert("Enter Value")
}

完整示例：-

 $(function () {

         $('#myButton').on('click', function () {

             var lvl = $('#MainContent_txtProductConstruction').val()
                if(lvl.length>0)
                {
             $.ajax({
                 type: "POST",
                 url: "NewProductConstruction.aspx/GetCollection",

                 data: JSON.stringify({'lvl': lvl }),

                 contentType: "application/json; charset=utf-8",
                 dataType: "json",

                 success: function (response) {
                     alert("Saved successfully.");
                     console.log(response);
                     location.reload(true);

                 },
                 error: function (response) {
                     alert("Not Saved!");
                     console.log(response);
                     location.reload(true);
                 }
             });
             }
            else
            {
            alert("Please enter Value")
            }
         });

     });

第二部分：-

sqlCommand checkvalue = new sqlCommand("SELECT COUNT(*) FROM [TableName] WHERE ([ColumnNameUser] = @user)" , connection);
checkvalue.Parameters.AddWithValue("@user", lvl);
int UserExist = (int)checkvalue.ExecuteScalar();

if(UserExist > 0)
{
   //Username exist
}
else
{
   //Username doesn't exist.
}

Reference Link

如果您想让Sp检查,则：-

根据您的姓名和字段名称进行编辑.

CREATE PROCEDURE InsertName
(
  @username varchar(25), 
  @userpassword varchar(25)
)
AS
IF EXISTS(SELECT 'True' FROM MyTable WHERE username = @username)
BEGIN
  --This means it exists, return it to ASP and tell us
  SELECT 'This record already exists!'
END
ELSE
BEGIN
  --This means the record isn't in there already, let's go ahead and add it
  SELECT 'Record Added'
  INSERT into MyTable(username, userpassword) VALUES(@username, @userpassword)
END