Development Hints from Bulgaria

Friday, April 4, 2014

Skipping constraint checks in MySQL

Error
Cannot delete or update a parent row: a foreign key constraint fails

Issue:
mysql> update User SET id=6 where id = 8;

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`database_name`.`table_name`, CONSTRAINT `FK_35jtu0049tkg8m9twhc03ii9` FOREIGN KEY (`customer`) REFERENCES `user` (`id`))

Solution:
SET foreign_key_checks = 1;
; execute code with constraint restrictions here
SET foreign_key_checks = 0;

Hibernate: setting foreigh key without getting foreign object

A nice solution from stackoverflow:
http://stackoverflow.com/questions/21012293/hibernate-add-entity-with-child-entity-id

Tuesday, March 25, 2014

Java IO Tutorial - file read / write

Commonly Used Methods for Small Files

Reading All Bytes or Lines from a File

If you have a small-ish file and you would like to read its entire contents in one pass, you can use the readAllBytes(Path) or readAllLines(Path, Charset) method. These methods take care of most of the work for you, such as opening and closing the stream, but are not intended for handling large files. The following code shows how to use the readAllBytes method:

Path file = ...;
byte[] fileArray;
fileArray = Files.readAllBytes(file);

Writing All Bytes or Lines to a File

The following code snippet shows how to use a write method.

Path file = ...;
byte[] buf = ...;
Files.write(file, buf);

Original tutorial is locate here: http://docs.oracle.com/javase/tutorial/essential/io/file.html

Thursday, March 20, 2014

Getting last element in Hibernate's repository by annotations

Getting last element in hibernate is useful for integration testing, where you have to ensure some object is stored in database, for example.

Using Hibernate SQL.

Code:
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.jpa.repository.Query;

public interface MyObjectRepository extends CrudRepository<MyObject, Long> {

@Query("FROM com.yourcompany.zzz.MyObject c WHERE (c.id) IN (select max(id) from com.yourcompany.zzz.MyObject)")
MyObject getLastOne();

}

It returns null, when there are no elements in table (do not throw an exception).

Tuesday, March 11, 2014

junit 4 in 60 seconds

Perfect article with examples for junit 4.

Wednesday, March 5, 2014

Blank template JavaScript application for JSON requests

Blank template application for JSON requests with and without body:

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>My Blank JS / jQuery app - jsFiddle demo by jorooo</title>

<script type='text/javascript' src='http://code.jquery.com/jquery-latest.js'></script>

<script type='text/javascript' src="http://code.jquery.com/mobile/latest/jquery.mobile.min.js"></script>
<link rel="stylesheet" type="text/css" href="http://code.jquery.com/mobile/latest/jquery.mobile.min.css">

<style type='text/css'>

</style>
</head>
<body>
<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
    $("#alert").bind("click", function(event) {
        alert('alert called');
    });

    $("#call_json_with_body").bind("click", function(event) {
        $.ajax({
            success: function( data ){
                alert("success");
                alert('success, data received is ' + JSON.stringify(data));
            },
            error: function( jqXHR, textStatus, errorThrown ){
                alert( "error while making ajax call. Error parameters are, " +
                    "\ntextStatus: " + textStatus +
                    ";\n errorThrown: " + errorThrown +
                    ";\n jqXHR: " + JSON.stringify(jqXHR) );
            },
            beforeSend: function(req) {
                req.setRequestHeader("Accept", "application/json");
                req.setRequestHeader("Content-Type","application/json");
            },
            dataType: 'json',
            data: JSON.stringify( {"zzz":"222"} ),
            type: 'POST',
            cache: false,
            url: "http://localhost:8080/add_venue_raw",
          }
        );
    });
    $("#call_json_without_body").bind("click", function(event) {
        $.ajax({
            success: function( data ){
                alert("x");
                alert('success, data received is ' + JSON.stringify(data) );
            },
            error: function( jqXHR, textStatus, errorThrown ){
                alert( "error while making ajax call. Error parameters are, " +
                    "\ntextStatus: " + textStatus +
                    ";\n errorThrown: " + errorThrown +
                    ";\n jqXHR: " + JSON.stringify(jqXHR) );
            },
            type: 'GET',
            cache: false,
            url: "http://localhost:8080/user/1",
          }
        );
    });
});//]]>

</script>

<div data-role="page" id="p1">
    <div data-role="header"><h1>Header</h1></div>

    <div data-role="content">
        <h5>If the script is running from a file:/// URL you could experience some issues. It's best not to do AJAX requests from file URLs, because they are treated inconsistently. Chrome, for example, entirely disallows them. Firefox also.</h5>
        <a href="#" id="call_json_without_body" data-role="button">JSON request without body</a><br/>
        <a href="#" id="call_json_with_body" data-role="button">JSON request with body</a><br/>
        <a href="#" id="alert" data-role="button">Show alert</a>
    </div>

    <div data-role="footer"><h4>Footer</h4></div>
</div>

</body>
</html>

static root folder for maven projects

Static files could be copied here:
<maven-project-root>\src\main\webapp\resources

They are accessed on server on URL:
<server_address>/resources

Example:
<maven-project-root>\src\main\webapp\resources\x.txt
could be accessed on
http://localhost:8080/resources/x.txt

In come cases, the content changes are actualized without server restart. For example with:
mvn jetty:run