Php – Get Specific Columns Using “With()” Function in Laravel Eloquent

eloquentlaravellaravel-query-builderormPHP

I have two tables, User and Post. One User can have many posts and one post belongs to only one user.

In my User model I have a hasMany relation…

public function post(){
    return $this->hasmany('post');
}

And in my post model I have a belongsTo relation…

public function user(){
    return $this->belongsTo('user');
}

Now I want to join these two tables using Eloquent with() but want specific columns from the second table. I know I can use the Query Builder but I don't want to.

When in the Post model I write…

public function getAllPosts() {
    return Post::with('user')->get();
}

It runs the following queries…

select * from `posts`
select * from `users` where `users`.`id` in (<1>, <2>)

But what I want is…

select * from `posts`
select id,username from `users` where `users`.`id` in (<1>, <2>)

When I use…

Post::with('user')->get(array('columns'....));

It only returns the column from the first table. I want specific columns using with() from the second table. How can I do that?

Best Answer

Well I found the solution. It can be done one by passing a closure function in with() as second index of array like

Post::query()
    ->with(array('user' => function($query) {
        $query->select('id','username');
    }))
    ->get();

It will only select id and username from other table. I hope this will help others.

Remember that the primary key (id in this case) needs to be the first param in the $query->select() to actually retrieve the necessary results.*

Related Solutions

Php – How to do ‘insert if not exists’ in MySQL

Use INSERT IGNORE INTO table.

There's also INSERT … ON DUPLICATE KEY UPDATE syntax, and you can find explanations in 13.2.6.2 INSERT ... ON DUPLICATE KEY UPDATE Statement.

Post from bogdan.org.ua according to Google's webcache:

18th October 2007

To start: as of the latest MySQL, syntax presented in the title is not possible. But there are several very easy ways to accomplish what is expected using existing functionality.

There are 3 possible solutions: using INSERT IGNORE, REPLACE, or INSERT … ON DUPLICATE KEY UPDATE.

Imagine we have a table:
CREATE TABLE `transcripts` (
`ensembl_transcript_id` varchar(20) NOT NULL,
`transcript_chrom_start` int(10) unsigned NOT NULL,
`transcript_chrom_end` int(10) unsigned NOT NULL,
PRIMARY KEY (`ensembl_transcript_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Now imagine that we have an automatic pipeline importing transcripts meta-data from Ensembl, and that due to various reasons the pipeline might be broken at any step of execution. Thus, we need to ensure two things:

repeated executions of the pipeline will not destroy our > database

repeated executions will not die due to ‘duplicate > primary key’ errors.

Method 1: using REPLACE

It’s very simple:
REPLACE INTO `transcripts`
SET `ensembl_transcript_id` = 'ENSORGT00000000001',
`transcript_chrom_start` = 12345,
`transcript_chrom_end` = 12678;
If the record exists, it will be overwritten; if it does not yet exist, it will be created. However, using this method isn’t efficient for our case: we do not need to overwrite existing records, it’s fine just to skip them.

Method 2: using INSERT IGNORE Also very simple:
INSERT IGNORE INTO `transcripts`
SET `ensembl_transcript_id` = 'ENSORGT00000000001',
`transcript_chrom_start` = 12345,
`transcript_chrom_end` = 12678;
Here, if the ‘ensembl_transcript_id’ is already present in the database, it will be silently skipped (ignored). (To be more precise, here’s a quote from MySQL reference manual: “If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted.”.) If the record doesn’t yet exist, it will be created.

This second method has several potential weaknesses, including non-abortion of the query in case any other problem occurs (see the manual). Thus it should be used if previously tested without the IGNORE keyword.

Method 3: using INSERT … ON DUPLICATE KEY UPDATE:

Third option is to use INSERT … ON DUPLICATE KEY UPDATE syntax, and in the UPDATE part just do nothing do some meaningless (empty) operation, like calculating 0+0 (Geoffray suggests doing the id=id assignment for the MySQL optimization engine to ignore this operation). Advantage of this method is that it only ignores duplicate key events, and still aborts on other errors.

As a final notice: this post was inspired by Xaprb. I’d also advise to consult his other post on writing flexible SQL queries.

Php – Reference — What does this symbol mean in PHP

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

Stack Overflow Posts:

Understanding Incrementing

Best Answer

Related Solutions

Php – How to do ‘insert if not exists’ in MySQL

Php – Reference — What does this symbol mean in PHP

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