OdbcDataReader.GetBoolean（）引发转换的奇怪问题不是布尔列的有效异常

Question

Ok, this one is driving me completely crazy. I have a table in a PostgreSQL database and I'm trying to get the value a boolean column for a specific record with OdbcDataReader.GetBoolean(int col).

The problem is that GetBoolean() keeps throwing a cast is not valid exception even though the same code worked just several days ago. What's even weirder is the same code works fine in another form.

The only change made from the previous working version of my application was adding a column to the table. That said, the index of the column that I need hasn't changed. Oh yeah, getting the value with GetValue() and then calling GetType() on the result returns System.String and the true/false values get translated to 1/0.

I'm all out of ideas.

Answer 1

While I still have no idea what is causing this exception, I've managed to come up with code that works (not actual code from my app):

val1 = reader.GetInt32(0);
val2 = reader.GetBoolean(4);
val3 = reader.GetBoolean(8);

This, however, does not:

val3 = reader.GetBoolean(8);
val1 = reader.GetInt32(0); // causes invalid cast exception
val2 = reader.GetBoolean(4);

Apparently, the column order has something to do with it.

Answer 2

I don't think passing a System.String to GetBoolean() is going to work for you - as you can see from your exception you're getting an InvalidCastException, which means that internally somewhere it's trying to do something like this:

string s = "true";
bool b = (bool)s;

That clearly won't work.

If you can see that ODBC is passing you back a System.String then you want to use either Convert.ToBoolean(), bool.TryParse(), or bool.Parse, depending on what exactly fits best with the rest of your code.

As to why it WAS working and now isn't - has someone else changed the underlying data type on the database field to a character-based type?

This pattern is what we use to get boolean data out of an OdbcDataReader:

data.Gender = reader["Gender"] == DBNull.Value ? 
    false : Convert.ToBoolean(reader["Gender"]);

Laborious, yes. But it works well for us. The underlying database for this code is Access ("yes/no" field type) or MS SQL Server ("bit" field type).

Answer 3

I ran into the same issue, it was actually due to an invalid cast I had in the SP I was calling...

IN the Stored Proc

declare @colA INT -- should have been a float!!!
set @colA = select someValue from someTable

select @someVar, someColumn
from someOtherTable

 //the line below works, even though it should have the SQL datatype is FLOAT
 _someVar = reader[2] != DBNull.Value ? reader.GetDouble[2] : 0;
  //the following line blows up w/invalid cast exception, even though it is correct
 _someColumn = reader[3] != DBNull.Value ? reader.GetBoolean[3] : false;