INSERT QUERY ERROR--> Recoverable fatal error: Object of class mysqli could not be converted to string in : i have been 3 hours stuck in this code, after the submit button was clicked, the record was not stored. All syntax i have look through, all look fine. Where is the thing againsting it to insert? Help please... cuz most of the guidance i look through almost is because select statement, but now i'm insert statement and same issue occur. here's my code:

    <table border='1'>
    			<tr>
    				<th colspan="2">
    					<h1>Property For Rent</h1>
    				</th>
    			<form method="post">
    				<tr><td>Property NO:</td><td><input type="textbox" name="pid"></td></tr>
    				<tr><td>Street:</td><td><input type="textbox" name="street"></td></tr>
    				<tr><td>City:</td><td><input type="textbox" name="city"></td></tr>
    				<tr><td>Post Code:</td><td><input type="textbox" name="postcode"></td></tr>
    				<tr><td>Type:</td><td><input type="textbox" name="type"></td></tr>
    				<tr><td>Rooms:</td><td><input type="textbox" name="rooms"></td></tr>
    				<tr><td>Rent:</td><td><input type="textbox" name="rent"></td></tr>
    				<tr><td>Owner No:</td><td><select name="ownerno">
    							<?php 
    								$conon=mysqli_connect('localhost','root','','dreamhome');
    								$SQLon="select distinct ownerNo from propertyforrent";
    								$queryresulton = mysqli_query($conon,$SQLon);
    								while($resulton=mysqli_fetch_array($queryresulton))
    								{
    									echo '<option value=" '.$resulton['ownerNo'].' ">'.$resulton['ownerNo'].'</option>';
    								}
    								?>
    							</td></tr>
    				<tr><td>Staff No:</td><td><select name="staffno">
    							<?php 
    								$consn=mysqli_connect('localhost','root','','dreamhome');
    								$SQLsn="select distinct staffNo from propertyforrent";
    								$queryresultsn = mysqli_query($consn,$SQLsn);
    								while($resultsn=mysqli_fetch_array($queryresultsn))
    								{
    									echo '<option value=" '.$resultsn['staffNo'].' ">'.$resultsn['staffNo'].'</option>';
    								}
    								?>
    							</td></tr>
    				<tr><td>Branch No:</td><td><select name="branchno">
    							<?php 
    								$conbn=mysqli_connect('localhost','root','','dreamhome');
    								$SQLbn="select distinct branchNo from propertyforrent";
    								$queryresultbn = mysqli_query($conbn,$SQLbn);
    								while($resultbn=mysqli_fetch_array($queryresultbn))
    								{
    									echo '<option value=" '.$resultbn['branchNo'].' ">'.$resultbn['branchNo'].'</option>';
    								}
    								?>
    							</td></tr>
    				<td><input type="Submit" name="submit">
    							
    							</td>
    			</form>
    		</table>
    					<?php
    					if(isset($_POST['submit']))
    					{
    						if((!empty($_POST['pid']))&&(!empty($_POST['street']))&&(!empty($_POST['city']))
    						&&(!empty($_POST['postcode']))&&(!empty($_POST['type']))&&(!empty($_POST['rooms']))&&(!empty($_POST['rent']))
    						&&(!empty($_POST['ownerno']))&&(!empty($_POST['staffno']))&&(!empty($_POST['branchno'])))
    						{
    							$conad=mysqli_connect('localhost','root','','dreamhome');
    							if(!$conad)
    							{
    									echo 'Note connected to server';
    							} 
    							
    							if(!mysqli_select_db($conad,'dreamhome'))
    							{
    								echo 'Database Not Selected';
    							}
    							
    							$pid=mysqli_real_escape_string($conad,$_POST['pid']);
    							$street=mysqli_real_escape_string($conad,$_POST['street']);
    							$city=mysqli_real_escape_string($conad,$_POST['city']);
    							$postcode=mysqli_real_escape_string($conad,$_POST['postcode']);
    							$type=mysqli_real_escape_string($conad,$_POST['type']);
    							$rooms=mysqli_real_escape_string($conad,$_POST['rooms']);
    							$rent=mysqli_real_escape_string($conad,$_POST['rent']);
    							$ownerno=mysqli_real_escape_string($conad,$_POST['ownerno']);
    							$staffno=mysqli_real_escape_string($conad,$_POST['staffno']);
    							$branchno=mysqli_real_escape_string($conad,$_POST['branchno']);
    							
    							$SQLad= "INSERT INTO propertyforrent (propertyNo,street,city,postcode,type,rooms,rent,ownerNo,staffNo,branchNo)
    									VALUES ('$pid','$street','$city','$postcode','$type','$rooms','$rent','$ownerno','$staffno','$branchno')";
    							$resultad=mysqli_query($conad,$SQLad);
    							
    							if(!$resultad)
    							{
    								echo "record not save!,mysqli_error($SQLad)";
    							}
    							else
    							{
    								echo "record save!";
    							}
    						}
    						else
    						{
    							echo "<h1>Please fill up all field!</h1>";
    						}
    						
    					
    					}
    					?>



The error prompted out from mysqli_error is 

> Recoverable fatal error: Object of class mysqli could not be converted
> to string in