After a numerous try and error, I've found out that it is not possible to do this using where clause

`componentDidMount() {

    this.unsubscribe1 = this.ref.onSnapshot(this.onCollectionUpdate1);

    this.unsubscribe2 = this.refAssign.where(‘email’, ‘==’, this.state.user.email ).onSnapshot(this.onCollectionUpdate2);

}`

instead of that, I compare it in render using condition ? true : false

                        {this.state.user.map(user =>

                          <tr>

                            <td><Link to={`/show/${user.key}`}>{user.email}</Link></td>

                            <td>{user.name}</td>

                            <td>{user.authority}</td>

                            <td>

                            {this.state.assign.map(assign =>

                                <p>{assign.email == user.email ? assign.projNo : null }</p>

                            )}

                            </td>

                          </tr>

                        )}