参数化查询... . . 期望得到未提供的参数“@unit”

我有个例外:

参数化查询’(@Name nvarchar (8)、@type nvarchar (8)、@unit nvarchar (4000)、@range’需要未提供的参数‘@unit’。

我的插入代码是:

public int insertType(string name, string type, string units = "N\\A", string range = "N\\A", string scale = "N\\A", string description = "N\\A", Guid guid = new Guid())
{
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
SqlCommand command = new SqlCommand();
command.CommandText = "INSERT INTO Type(name, type, units, range, scale, description, guid) OUTPUT INSERTED.ID VALUES (@Name, @type, @units, @range, @scale, @description, @guid) ";
command.Connection = connection;
command.Parameters.AddWithValue("@Name", name);
command.Parameters.AddWithValue("@type", type);
command.Parameters.AddWithValue("@units", units);
command.Parameters.AddWithValue("@range", range);
command.Parameters.AddWithValue("@scale", scale);
command.Parameters.AddWithValue("@description", description);
command.Parameters.AddWithValue("@guid", guid);
return (int)command.ExecuteScalar();
}
}

这个异常令人惊讶，因为我正在使用 AddWithValue函数并确保为该函数添加了默认参数。

解决了:

问题是一些空 String (覆盖默认值)的参数

这是工作代码:

public int insertType(string name, string type, string units = "N\\A", string range = "N\\A", string scale = "N\\A", string description = "N\\A", Guid guid = new Guid())
{
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
SqlCommand command = new SqlCommand();
command.CommandText = "INSERT INTO Type(name, type, units, range, scale, description, guid) OUTPUT INSERTED.ID VALUES (@Name, @type, @units, @range, @scale, @description, @guid) ";
command.Connection = connection;
command.Parameters.AddWithValue("@Name", name);
command.Parameters.AddWithValue("@type", type);


if (String.IsNullOrEmpty(units))
{
command.Parameters.AddWithValue("@units", DBNull.Value);
}
else
command.Parameters.AddWithValue("@units", units);
if (String.IsNullOrEmpty(range))
{
command.Parameters.AddWithValue("@range", DBNull.Value);
}
else
command.Parameters.AddWithValue("@range", range);
if (String.IsNullOrEmpty(scale))
{
command.Parameters.AddWithValue("@scale", DBNull.Value);
}
else
command.Parameters.AddWithValue("@scale", scale);
if (String.IsNullOrEmpty(description))
{
command.Parameters.AddWithValue("@description", DBNull.Value);
}
else
command.Parameters.AddWithValue("@description", description);








command.Parameters.AddWithValue("@guid", guid);




return (int)command.ExecuteScalar();
}




}

105910

小开

最佳答案

Try this code:

SqlParameter unitsParam = command.Parameters.AddWithValue("@units", units);
if (units == null)
{
unitsParam.Value = DBNull.Value;
}

And you must check all other parameters for null value. If it null you must pass DBNull.Value value.

小开

Here's a way using the null-coalescing operator:

cmd.Parameters.AddWithValue("@units", units ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@range", range ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@scale", scale ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@description", description ?? (object)DBNull.Value);

Or for more strict type checking:

cmd.Parameters.Add("@units", SqlDbType.Int).Value = units ?? (object)DBNull.Value;
cmd.Parameters.Add("@range", SqlDbType.Int).Value = range ?? (object)DBNull.Value;
cmd.Parameters.Add("@scale", SqlDbType.Int).Value = scale ?? (object)DBNull.Value;
cmd.Parameters.Add("@description", SqlDbType.VarChar).Value = description ?? (object)DBNull.Value;

The operator also be chained:

int?[] a = { null, null, 1 };
Console.WriteLine(a[0] ?? a[1] ?? a[2]);

小开

This is a method to be reused with multiple parameters:

public void NullorEmptyParameter(QC.SqlCommand command, string at, string value)
{
if (String.IsNullOrEmpty(value))
{
command.Parameters.AddWithValue(at, DBNull.Value);
}
else
command.Parameters.AddWithValue(at, value);
}

And then you can reuse it for as many commands and params:

NullorEmptyParameter(command, "@Idea_ID", Idea_ID);
NullorEmptyParameter(command, "@Opportunities_or_Idea", Opportunities_or_Idea);

小开

command.Parameters.AddWithValue("@Name", (name == null ? "" : name));

小开

This extension class was useful to me a couple of times so far, for those issues:

public static class DbValueExtensions
{
// Used to convert values coming from the db
public static T As<T>(this object source)
{
return source == null || source == DBNull.Value
? default(T)
: (T)source;
}


// Used to convert values going to the db
public static object AsDbValue(this object source)
{
return source ?? DBNull.Value;
}
}

You would normally use it in two scenarios. First, when creating parameters for your query:

var parameters = new Dictionary<string, object>
{
{ "@username", username.AsDbValue() },
{ "@password", password.AsDbValue() },
{ "@birthDate", birthDate.AsDbValue() },
};

or when parsing the SqlReader values:

while (reader.Read())
{
yield return new UserInfo(
reader["username"].As<string>(),
reader["birthDate"].As<DateTime>(),
reader["graduationDate"].As<DateTime?>(),
reader["nickname"].As<string>()
);
}