asked on

Attempted to read or write protected memory. this is often an indication that other memory is corrupt.

Hello Experts,

I am running MySQL (installed the latest version about 2 months ago) on a windows 2000 server. I am connected to it through the MySQL ODBC version 3.51.12.

I am connecting to it through Visual Studio 2005 (VS) using VB.net on an Win XP client computer. VB works fine in reading the tables and data, writing to the DB and so on. Then, all of sudden I started getting the above error. Looking around on the Internet others seem to have had this problem but no -one seems to have posted a solution that I have found.

Any help greatly appreciated. This is urgent because if I can't fix this I'll have to throw away most of my development and start again with another DB. Aside from the loss in development time, I like MySQL and so I am really hoping an incompatibility between the MySQL ODBC and VB.Net does not become a problem.

This is the line that the error occurs on:
            Dim CustomersChanges As DStruWest.CustomersDataTable = gDS.Customers.GetChanges()
            If Not CustomersChanges Is Nothing Then Me.CustomersTableAdapter.Update(CustomersChanges) ' ERROR ********************
This gives the same result: Me.CustomersTableAdapter.Update(DStruWest.CustomersDataTable)

When I trace all the auto-generated code it is the last line of the routine (upon returning from it) that the error actually occurs:
<System.Diagnostics.DebuggerNonUserCodeAttribute()> _
Private ReadOnly Property Adapter() As System.Data.Odbc.OdbcDataAdapter
Get
If (Me._adapter Is Nothing) Then
Me.InitAdapter
            End If
            Return Me._adapter
End Get
End Property

Here is the stack trace:
" at System.Data.Common.UnsafeNativeMethods.SQLExecDirectW(OdbcStatementHandle StatementHandle, String StatementText, Int32 TextLength)
at System.Data.Odbc.OdbcCommand.ExecuteReaderObject(CommandBehavior behavior, String method, Boolean needReader, Object[] methodArguments, SQL_API odbcApiMethod)
at System.Data.Odbc.OdbcCommand.ExecuteReaderObject(CommandBehavior behavior, String method, Boolean needReader)
at System.Data.Odbc.OdbcCommand.ExecuteReader(CommandBehavior behavior)
at System.Data.Odbc.OdbcCommand.ExecuteDbDataReader(CommandBehavior behavior)
at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.UpdateRowExecute(RowUpdatedEventArgs rowUpdatedEvent, IDbCommand dataCommand, StatementType cmdIndex)
at System.Data.Common.DbDataAdapter.Update(DataRow[] dataRows, DataTableMapping tableMapping)
at System.Data.Common.DbDataAdapter.UpdateFromDataTable(DataTable dataTable, DataTableMapping tableMapping)
at System.Data.Common.DbDataAdapter.Update(DataTable dataTable)
at truWest.DStruWestTableAdapters.CustomersTableAdapter.Update(CustomersDataTable dataTable)
at truWest.Customer.SaveData()"

newyuppie

what is the exception message thrown?

RegProctor

ASKER

The exception message is:
Message "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

and ex.gettype() returns:

?ex.GetType
{Name = "AccessViolationException" FullName = "System.AccessViolationException"}
System.RuntimeType: {Name = "AccessViolationException" FullName = "System.AccessViolationException"}
Assembly: {System.Reflection.Assembly}
AssemblyQualifiedName: "System.AccessViolationException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
Attributes: 1056769
BaseType: {Name = "SystemException" FullName = "System.SystemException"}
ContainsGenericParameters: False
DeclaringMethod: {"Method may only be called on a Type for which Type.IsGenericParameter is true."}
DeclaringType: Nothing
DefaultBinder: {System.DefaultBinder}
Delimiter: "."c
EmptyTypes: {Length=0}
FilterAttribute: {System.Reflection.MemberFilter}
FilterName: {System.Reflection.MemberFilter}
FilterNameIgnoreCase: {System.Reflection.MemberFilter}
FullName: "System.AccessViolationException"
GenericParameterAttributes: {"Method may only be called on a Type for which Type.IsGenericParameter is true."}
GenericParameterPosition: {"Method may only be called on a Type for which Type.IsGenericParameter is true."}
GUID: {System.Guid}
HasElementType: False
IsAbstract: False
IsAnsiClass: True
IsArray: False
IsAutoClass: False
IsAutoLayout: True
IsByRef: False
IsClass: True
IsCOMObject: False
IsContextful: False
IsEnum: False
IsExplicitLayout: False
IsGenericParameter: False
IsGenericType: False
IsGenericTypeDefinition: False
IsImport: False
IsInterface: False
IsLayoutSequential: False
IsMarshalByRef: False
IsNested: False
IsNestedAssembly: False
IsNestedFamANDAssem: False
IsNestedFamily: False
IsNestedFamORAssem: False
IsNestedPrivate: False
IsNestedPublic: False
IsNotPublic: False
IsPointer: False
IsPrimitive: False
IsPublic: True
IsSealed: False
IsSerializable: True
IsSpecialName: False
IsUnicodeClass: False
IsValueType: False
IsVisible: True
MemberType: TypeInfo {32}
MetadataToken: 33554500
Missing: {System.Reflection.Missing}
Module: {System.Reflection.Module}
Name: "AccessViolationException"
Namespace: "System"
ReflectedType: Nothing
StructLayoutAttribute: {System.Runtime.InteropServices.StructLayoutAttribute}
TypeHandle: {System.RuntimeTypeHandle}
TypeInitializer: Nothing
UnderlyingSystemType: {Name = "AccessViolationException" FullName = "System.AccessViolationException"}

RegProctor

ASKER

Here's some further information:

To much relief, I have solved the problem and it could just be me being very green (a newbie) with vb.net.

Here's what I found, perhaps you could enlighten me a bit:

I have a child/parent relationship on a form. When I clicked on the BindingNavigatorAddNewItem object it did a normal insert.
If I then went to the child and inserted a row I got an error to the effect that "the value (-1) must exist in the parent". So, I rechecked how I set up the relationships and all seemed well. The -1 did exist on the parent but the child was not picking it up while the record had not yet been committed. So, I put some code in that did an update on the parent table as soon as the DataGridVew (which held the child records) got the focus. Now inserting rows in the DGV no longer caused errors. Great.

Then this error started happening when I went to close the form and update everything (as the code above shows). However, I just had an idea that solved it. Right after I do an update on the parent table from the DGV getting the focus I also do an AcceptChanges. This works. What I am unsure of is why. It was my belief (remember I am very green) that the DataSet was very good at keeping track of what has been done and what needs to be done that calling AcceptChanges should be used in a very sparingly manner.

On the other hand it works and that's the most important thing at this point.

I'm wondering now if I should put an AcceptChanges after all the .update calls.

newyuppie

generally, the .Update method will issue an AcceptChanges call by default, unless you specify that it not do that (via the AcceptChangesDuringUpdate property - http://msdn2.microsoft.com/en-us/library/system.data.common.dataadapter.acceptchangesduringupdate.aspx)

on the issue of the -1 must exist, im guessing it has something to do with the way your dataset is updating its changes. When you add a new child, you have probably set an autonumber column to be the Private Key, and its probably set to start at -1 and substract 1 for each new record (the AutoIncrementSeed and AutoIncrementStep properties of the DataColumn - http://msdn2.microsoft.com/en-us/library/system.data.datacolumn.autoincrement.aspx). This will return errors if you haven't correctly set the method of Update (try reading this http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=189482&SiteId=1)

hope it was helpful
NY

RegProctor

ASKER

The Child table has its own primary key (I gather you meant primary key, not private key, otherwise please do enlighten me) and so does the parent table. A non-autoincrementing field in the child table points to the parent table's primary key (PK). As I understand it the DataSet is smart enough to keep new child table entries in sync with the parent table's PK. And this is seems to be doing because it's looking for -1 and that is what it will be in the parent table at the time it looks for it. The problem is that the child table doesn't see that the parent table has the -1 value and I assumed that was because I needed to do an Update to make it viewable. I could try doing just an EndEdit on the parent table instead, I haven't tried that yet.

You are right, all that I had read suggested to set the AutoIncrementSeed and AutoIncrementStep properties to -1 and I have done so to avoid collisions with the DB.

I also have some code in a RowUpdated event of the table adapter that gets the real PK from the database when it is actually written to so as the keep the DataSet in sync with the DB. This I found necessary for successive add/deletes.

RegProctor

ASKER

Oops. I take that back. It was actually EndEdit that I was doing already.

RegProctor

ASKER

I found it! Ladies and gents, it was in the DataSet designer being internally corrupted. Once I removed the parent table and added it back things were better. When I removed the child table after that and added it back, it finally worked!

For anyone who gets weird errors like this. Try removing the whole table and it's adapter and adding it back again.

ASKER CERTIFIED SOLUTION

DarthMod

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