Question

DataTable.Rows.Add() adds a row to the data table. However, how does it handle the underlying array?

When adding a single row at a time, does it rebuild the entire array with each row added?

Or is it able to simply modify the existing array without any hit on performance?

I am wondering if it’s better to determine the size of the array before filling it with data, or if somehow the data table is able to modify the collection without (behind the scenes) copying and moving things.

It’s my understanding that to adjust an array you have to redefine it and move previously existing data into the new structure.

My question is what is the work flow for the Collection.Add() method?

Answer 1

Take a look using software like DotPeek:

DataTable.Rows.Add(DataRow row)
{
    this.table.AddRow(row, -1);
}

which calls:

DataTable.AddRow(DataRow row, int proposedID)
{
    this.InsertRow(row, proposedID, -1);
}

which calls:

DataTable.InsertRow(DataRow row, int proposedID, int pos)
{
    this.InsertRow(row, (long) proposedID, pos, true);
}  

which calls:

DataTable.InsertRow(DataRow row, long proposedID, int pos, bool fireEvent)
{
    Exception deferredException = (Exception) null;
    if (row == null)
        throw ExceptionBuilder.ArgumentNull("row");
    if (row.Table != this)
        throw ExceptionBuilder.RowAlreadyInOtherCollection();
    if (row.rowID != -1L)
        throw ExceptionBuilder.RowAlreadyInTheCollection();
    row.BeginEdit();
    int proposedRecord = row.tempRecord;
    row.tempRecord = -1;
    if (proposedID == -1L)
        proposedID = this.nextRowID;
    bool flag;
    if (flag = this.nextRowID <= proposedID)
        this.nextRowID = checked (proposedID + 1L);
    try
    {
        try
        {
            row.rowID = proposedID;
            this.SetNewRecordWorker(row, proposedRecord, DataRowAction.Add, false, false, pos, fireEvent, out deferredException);
        }
        catch
        {
            if (flag && this.nextRowID == proposedID + 1L)
                this.nextRowID = proposedID;
            row.rowID = -1L;
            row.tempRecord = proposedRecord;
            throw;
        }
        if (deferredException != null)
            throw deferredException;
        if (!this.EnforceConstraints || this.inLoad)
            return;
        int count = this.columnCollection.Count;
        for (int index = 0; index < count; ++index)
        {
            DataColumn dataColumn = this.columnCollection[index];
            if (dataColumn.Computed)
                dataColumn.CheckColumnConstraint(row, DataRowAction.Add);
        }
    }
    finally
    {
        row.ResetLastChangedColumn();
    }
}

which calls:

DataTable.SetNewRecordWorker(DataRow row, int proposedRecord, DataRowAction action, bool isInMerge, bool suppressEnsurePropertyChanged, int position, bool fireEvent, out Exception deferredException)
{
    deferredException = (Exception) null;
    if (row.tempRecord != proposedRecord)
    {
    if (!this.inDataLoad)
    {
        row.CheckInTable();
        this.CheckNotModifying(row);
    }
    if (proposedRecord == row.newRecord)
    {
        if (!isInMerge)
        return;
        this.RaiseRowChanged((DataRowChangeEventArgs) null, row, action);
        return;
    }
    else
        row.tempRecord = proposedRecord;
    }
    DataRowChangeEventArgs args = (DataRowChangeEventArgs) null;
    try
    {
    row._action = action;
    args = this.RaiseRowChanging((DataRowChangeEventArgs) null, row, action, fireEvent);
    }
    catch
    {
    row.tempRecord = -1;
    throw;
    }
    finally
    {
    row._action = DataRowAction.Nothing;
    }
    row.tempRecord = -1;
    int record = row.newRecord;
    int num = proposedRecord != -1 ? proposedRecord : (row.RowState != DataRowState.Unchanged ? row.oldRecord : -1);
    if (action == DataRowAction.Add)
    {
    if (position == -1)
        this.Rows.ArrayAdd(row);
    else
        this.Rows.ArrayInsert(row, position);
    }
    List<DataRow> cachedRows = (List<DataRow>) null;
    if ((action == DataRowAction.Delete || action == DataRowAction.Change) && (this.dependentColumns != null && this.dependentColumns.Count > 0))
    {
    cachedRows = new List<DataRow>();
    for (int index = 0; index < this.ParentRelations.Count; ++index)
    {
        DataRelation relation = this.ParentRelations[index];
        if (relation.ChildTable == row.Table)
        cachedRows.InsertRange(cachedRows.Count, (IEnumerable<DataRow>) row.GetParentRows(relation));
    }
    for (int index = 0; index < this.ChildRelations.Count; ++index)
    {
        DataRelation relation = this.ChildRelations[index];
        if (relation.ParentTable == row.Table)
        cachedRows.InsertRange(cachedRows.Count, (IEnumerable<DataRow>) row.GetChildRows(relation));
    }
    }
    if (!suppressEnsurePropertyChanged && !row.HasPropertyChanged && (row.newRecord != proposedRecord && -1 != proposedRecord) && -1 != row.newRecord)
    {
    row.LastChangedColumn = (DataColumn) null;
    row.LastChangedColumn = (DataColumn) null;
    }
    if (this.LiveIndexes.Count != 0)
    {
    if (-1 == record && -1 != proposedRecord && (-1 != row.oldRecord && proposedRecord != row.oldRecord))
        record = row.oldRecord;
    DataViewRowState recordState1 = row.GetRecordState(record);
    DataViewRowState recordState2 = row.GetRecordState(num);
    row.newRecord = proposedRecord;
    if (proposedRecord != -1)
        this.recordManager[proposedRecord] = row;
    DataViewRowState recordState3 = row.GetRecordState(record);
    DataViewRowState recordState4 = row.GetRecordState(num);
    this.RecordStateChanged(record, recordState1, recordState3, num, recordState2, recordState4);
    }
    else
    {
    row.newRecord = proposedRecord;
    if (proposedRecord != -1)
        this.recordManager[proposedRecord] = row;
    }
    row.ResetLastChangedColumn();
    if (-1 != record && record != row.oldRecord && (record != row.tempRecord && record != row.newRecord) && row == this.recordManager[record])
    this.FreeRecord(ref record);
    if (row.RowState == DataRowState.Detached && row.rowID != -1L)
    this.RemoveRow(row, false);
    if (this.dependentColumns != null)
    {
    if (this.dependentColumns.Count > 0)
    {
        try
        {
        this.EvaluateExpressions(row, action, cachedRows);
        }
        catch (Exception ex)
        {
        if (action != DataRowAction.Add)
            throw ex;
        deferredException = ex;
        }
    }
    }
    try
    {
    if (!fireEvent)
        return;
    this.RaiseRowChanged(args, row, action);
    }
    catch (Exception ex)
    {
    if (!ADP.IsCatchableExceptionType(ex))
        throw;
    else
        ExceptionBuilder.TraceExceptionWithoutRethrow(ex);
    }
}

which calls one of those:

DataRowCollection.ArrayAdd(DataRow row)
{
  row.RBTreeNodeId = this.list.Add(row);
}

DataRowCollection.ArrayInsert(DataRow row, int pos)
{
  row.RBTreeNodeId = this.list.Insert(pos, row);
}

this.list is of type DataRowCollection.DataRowTree, derived from RBTree<DataRow>.

private sealed class DataRowTree : RBTree<DataRow>

RBTree<DataRow> and RBTreeNodeId allows us to conclude that a Red-Black tree is being used!