How to get DataKeyNames in Nested Grid in asp.net

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C#

ASP.NET

Here I have created 3 GridViews named as dgvBranch, dgvCourse and dgvSubject. dgvCourse is parent of dgvSubject and dgvBranch is parent of dgvCourse. On click of "Delete" button of dgvSubject i want datakey of Selected Branch in dgvBranch , selected Course in dgvCourse and selected subject in dgvSubject.

<div class="table-responsive">
                                <asp:GridView ID="dgvBranch" runat="server" AutoGenerateColumns="false" CssClass="table table-bordered table-striped"
                                    DataKeyNames="BranchID" ShowHeader="false" OnRowDataBound="dgvBranch_RowDataBound">
                                    <Columns>
                                        <asp:BoundField DataField="BranchName" />
                                        
                                        <asp:TemplateField ShowHeader="False">
                                            <ItemTemplate>
                                                <asp:HiddenField ID="HFBranch" runat="server" Value='<%# Eval("BranchID") %>' />
                                                <asp:LinkButton ID="lnbAddCourse" runat="server" CausesValidation="false" Text="Add Course"
                                                    OnClick="lnbAddCourse_Click"></asp:LinkButton>
                                            </ItemTemplate>
                                        </asp:TemplateField>
                                        <asp:TemplateField ShowHeader="False">
                                            <ItemTemplate>
                                                <img alt="" style="cursor: pointer" src="../img/down.jpg" />
                                                    <asp:Panel ID="pnlOrders" runat="server" Style="display: none">
                                                    <asp:GridView ID="dgvCourse" runat="server" AutoGenerateColumns="False" DataKeyNames="CourseID"
                                                        CssClass="table table-bordered table-striped" OnRowDataBound="dgvCourse_RowDataBound">
                                                        <Columns>
                                                            <asp:BoundField HeaderText="Course Name" DataField="Name" />
                                                            
                                                            <asp:TemplateField ShowHeader="False">
                                                                <ItemTemplate>
                                                                    <asp:LinkButton ID="lnbDelete" runat="server" CausesValidation="false" Text="Delete"
                                                                        OnClick="lnbDeleteCourse_Click"></asp:LinkButton>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                            <asp:TemplateField ShowHeader="False">
                                                                <ItemTemplate>
                                                                    <asp:HiddenField ID="HFCourse" runat="server" Value='<%# Eval("CourseID") %>' />
                                                                    <asp:LinkButton ID="lnbAddSubject" runat="server" CausesValidation="false" Text="Add Subject"
                                                                        OnClick="lnbAddSubject_Click"></asp:LinkButton>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                            <asp:TemplateField ShowHeader="False">
                                                                <ItemTemplate>
                                                                    <img alt="" style="cursor: pointer" src="../img/show.jpg" />
                                                                    <asp:Panel ID="pnlSubject" runat="server" Style="display: none">
                                                                        <asp:GridView ID="dgvSubject" runat="server" AutoGenerateColumns="False" DataKeyNames="SubjectID"
                                                                            CssClass="table table-bordered table-striped" OnRowDataBound="dgvSubject_RowDataBound">
                                                                            <Columns>
                                                                                <asp:BoundField HeaderText="Subject Name" DataField="SubjectName" />
                                                                                <asp:TemplateField ShowHeader="False">
                                                                                    <ItemTemplate>
                                                                                        <asp:LinkButton ID="lnbDeleteSubject" runat="server" CausesValidation="false" Text="Delete"
                                                                                            OnClick="lnbDeleteSubject_Click"></asp:LinkButton>
                                                                                    </ItemTemplate>
                                                                                </asp:TemplateField>
                                                                            </Columns>
                                                                        </asp:GridView>
                                                                    </asp:Panel>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                        </Columns>
                                                    </asp:GridView>
                                                </asp:Panel>
                                            </ItemTemplate>
                                        </asp:TemplateField>
                                    </Columns>
                                </asp:GridView>
                            </div>