public List <IComparable> GetLastRowFromTable(TableDefinition tableDefinition)
{
Stack <long> pointers = new Stack <long>();
long dataPosition = tableDefinition.DataAddress;
pointers.Push(dataPosition);
while (PageIsFull(dataPosition, tableDefinition.GetRowSizeInBytes()))
{
dataPosition = PageLocationHelper.GetNextPagePointer(dataPosition);
pointers.Push(dataPosition);
}
using (FileStream fs = new FileStream(Constants.FILE_NAME, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (BinaryReader binaryReader = new BinaryReader(fs))
{
List <List <IComparable> > rowsFromLastPage = ReadDataFromPage(dataPosition, tableDefinition.ColumnDefinitions, binaryReader);
if (!rowsFromLastPage.Any())
{
//if there are no rows, then the last row is on the previous page
pointers.Pop(); //remove last pointer, which is a pointer to an empty page
long previousAddress = pointers.Pop();
rowsFromLastPage = ReadDataFromPage(previousAddress, tableDefinition.ColumnDefinitions, binaryReader);
}
return(rowsFromLastPage.Last());
}
}
}
/// <summary>
/// Checks if current page is full. If so, writes a pointer to the end of the page and
/// returns next available writeable address.
/// Otherwise, return current address
/// </summary>
/// <param name="address"></param>
/// <returns></returns>
private void WritePointerIfLastObjectOnPage(long address, int objectSize)
{
long nextPageAddress = PageLocationHelper.GetNextDivisbleNumber(address, Constants.Page_Size);
long load = address + (objectSize + Constants.Int64_Byte_Length);
bool willBeLastObjectOnPage = load + objectSize >= nextPageAddress - Constants.Int64_Byte_Length;
if (willBeLastObjectOnPage)
{
long nextPagePointer = GetNextUnclaimedDataPage();
using (FileStream fileStream = File.Open(Constants.FILE_NAME, FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
using (BinaryWriter binaryWriter = new BinaryWriter(fileStream))
{
binaryWriter.BaseStream.Position = nextPageAddress - Constants.Int64_Byte_Length;
binaryWriter.Write(nextPagePointer);
binaryWriter.BaseStream.Position = nextPagePointer;
binaryWriter.Write((short)0);
}
}
}
}
public long GetPointerToNextPage(long pageAddress)
{
long pointerToNextPage = PageLocationHelper.GetNextDivisbleNumber(pageAddress, Constants.Page_Size)
- Constants.Int64_Byte_Length;
using (FileStream fs = new FileStream(Constants.FILE_NAME, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (BinaryReader binaryReader = new BinaryReader(fs))
{
binaryReader.BaseStream.Position = pointerToNextPage;
long nextPageAddress = binaryReader.ReadInt64();
return(nextPageAddress);
}
}
}
public long GetFirstAvailableDataAddress(long dataStart, int objectSize)
{
while (PageIsFull(dataStart, objectSize))
{
dataStart = PageLocationHelper.GetNextPagePointer(dataStart);
}
using (FileStream fileStream = new FileStream(Constants.FILE_NAME, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
fileStream.Position = dataStart;
using (BinaryReader binaryReader = new BinaryReader(fileStream))
{
short numObjects = binaryReader.ReadInt16();
return(objectSize * numObjects + 2 + dataStart);//todo: use global 2 byte integer size
}
}
}
