指定的强制转换在C＃中无效

Question

I have a column which is of type bigint in the database table. I want it to retrieve and assign it to variable in C# as shown below in the example.

Example :

obj.Total1 = (Int32)reader["Slno"] != null ? (Int32)reader["Slno"] : 0;
obj.Total2 = (Int32)reader["Rlno"] != null ? (Int32)reader["Rlno"] : 0;

Note : Here Slno and Rlno are of type bigint in database table.

Error : Following is the error message.

Specified cast is not valid.

Answer 1

SQL的BigInt映射为C＃中的long ，而不是int 。

Answer 2

BigInt needs to be mapped to long which is the equivalent 64bit integer value in C#.

Also, you should alter your code to something like this:

int slnoCol = reader.GetOrdinal("Slno");
int rlnoCol = reader.GetOrdinal("Rlno");

obj.Total1 = !reader.IsDBNull(slnoCol) ? reader.GetInt64(slnoCol) : (long)0;
obj.Total2 = !reader.IsDBNull(rlnoCol) ? reader.GetInt64(rlnoCol) : (long)0;

EDIT:

After noticing your comment that Total1 and Total2 are int , you also need to change them to long

public long Total1 { get; set; }
public long Total2 { get; set; }

This is because int is a 32bit integer which cannot store the same max value as a 64bit integer which is what you are using in your table.

Answer 3

In my case I was getting a " specified cast is not valid ", when my table was empty.

so I changed my code like so:

while (reader.Read())
    max = reader.GetInt32(0);

Added a check for DBNull :

while (reader.Read())
    max = reader.IsDBNull(0) ? 0 : reader.GetInt32(0);