VB.NET和MySQL：显示MonthName的DataGrid错误

Question

Having trouble displaying MonthName in a DataGridView from data in MySQL

Query:

SELECT ItemName, Description, PurchaseDate, MONTHNAME(PurchaseDate) AS PurchaseMonth FROM tblItems

Error:

System.ArguementException:Parameter is not valid

Displaying the month number, using MONTH(PurchaseDate) works perfect but when I try to show the month name I get a datagrid error. When I run the SQL in MySQL it returns the expected results.

When I add in a DataError event it just shows a red exclimation mark in the fields where MONTHNAME(PurchaseDate) should be.

Answer 1

Solved it. Even though MonthName(PurchaseDate) worked when run directly against the database, I had to use Cast in the SQL string when passing in from VB.NET

Amended SQL:

SELECT ItemName, Description, PurchaseDate, CAST(MONTHNAME(PurchaseDate) AS CHAR) AS PurchaseMonth FROM tblItems

Answer 2

Why do you want to do that?

Just load the raw date and use format string to get the name

dim purchaseDate as DateTime = DateTime.Now

dim purchaseMonth as String = purchaseDate.Format("MMMM")
' or
dim purchaseMonth as String = String.Format("{0}", purchasDate")

Databindings also support formatting.

This method has the advantage, that it respects the locals from the users environment:

' english: July
' german:  Juli