[12.x] Add Eloquent Relationship Attributes

src/Illuminate/Database/Eloquent/Attributes/Relations/BelongsTo.php

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+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class BelongsTo implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var array<string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->name = $name;
+        $this->arguments = [$related, ...$arguments];
+
+        $this->arguments = array_pad($this->arguments, 4, null);
+
+        if ($this->arguments[1] === null) {
+            $this->arguments[1] = Str::snake(class_basename($this->related)).'_id';
+        }
+
+        if ($this->arguments[2] === null) {
+            $this->arguments[2] = 'id';
+        }
+
+        $this->arguments[3] = $this->relationName();
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::singular(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/BelongsToMany.php

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+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class BelongsToMany implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var array<string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->name = $name;
+        $this->arguments = [$related, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::plural(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/HasArguments.php

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+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+/**
+ * @internal
+ */
+trait HasArguments
+{
+    /**
+     * @return array<mixed>
+     */
+    public function relationArguments(): array
+    {
+        return $this->arguments;
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/HasMany.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class HasMany implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var array<string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->name = $name;
+        $this->arguments = [$related, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::plural(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/HasManyThrough.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class HasManyThrough implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var class-string
+     */
+    public string $through;
+
+    /**
+     * @var array<string|class-string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  class-string  $through
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, string $through, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->through = $through;
+        $this->name = $name;
+        $this->arguments = [$related, $through, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::plural(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/HasOne.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class HasOne implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var array<string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->name = $name;
+        $this->arguments = [$related, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::singular(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/HasOneThrough.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class HasOneThrough implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    /**
+     * @var class-string
+     */
+    public string $through;
+
+    /**
+     * @var array<string|class-string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  class-string  $through
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, string $through, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->through = $through;
+        $this->name = $name;
+        $this->arguments = [$related, $through, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::singular(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/MorphMany.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class MorphMany implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    public string $morphName;
+
+    /**
+     * @var array<string|class-string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, string $morphName, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->morphName = $morphName;
+        $this->name = $name;
+        $this->arguments = [$related, $morphName, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::plural(Str::camel(class_basename($this->related)));
+    }
+}

src/Illuminate/Database/Eloquent/Attributes/Relations/MorphOne.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Illuminate\Database\Eloquent\Attributes\Relations;
+
+use Attribute;
+use Illuminate\Support\Str;
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+final class MorphOne implements RelationAttribute
+{
+    use HasArguments;
+
+    /**
+     * @var class-string
+     */
+    public string $related;
+
+    public string $morphName;
+
+    /**
+     * @var array<string|class-string>
+     */
+    public array $arguments = [];
+
+    private ?string $name;
+
+    /**
+     * @param  class-string  $related
+     * @param  array<string>  ...$arguments
+     */
+    public function __construct(string $related, string $morphName, ?string $name = null, string ...$arguments)
+    {
+        $this->related = $related;
+        $this->morphName = $morphName;
+        $this->name = $name;
+        $this->arguments = [$related, $morphName, ...$arguments];
+    }
+
+    public function relationName(): string
+    {
+        return $this->name ?? Str::singular(Str::camel(class_basename($this->related)));
+    }
+}