illegal assignment from list recordtype to string

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Illegal assignment from List<AggregateResult> to List<AggregateResult> #2763

eq-dsolari commented Nov 25, 2020

lcampos commented Nov 30, 2020

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Type Casting in Apex

Hello devs,

What are Upcasting and Downcasting? How can you cast Apex Map, List, and Set? What is a supertype, and what is the difference between SObject and Object? Answers to these questions and much more can be found in this post!

Let's begin.

Before We Start

I am using different emojis to grab your attention:

• 🚨 - Unexpected casting behavior.
• ✅ - Code that works.
• ❌ - Code that does not work.

What supertype is?

A supertype is an abstract/virtual class or an interface that is used by a child class.

The Parent interface is a supertype for the Child class.

A class can implements many interfaces, meaning that a class can have many supertypes .

The Parent abstract class is a supertype/superclass for the Child class.

A class can extends only one abstract class, but it can still implements many interfaces.

The Parent virtual class is a supertype/superclass for the Child class.

A class can extends only one virtual class, but it can still implements many interfaces.

Upcasting vs Downcasting

You know what supertype is, it's necessary to understand the difference between Upcasting and Downcasting .

To better understand upcasting and downcasting, we need some examples.

We have two classes (it can be also class and interface), Parent and Child .

• Parent is a virtual class and has a virtual method.
• Child extends the Parent class and override the virtual method.

If you don't understand what virtual means, you can refer to the Abstract, Virtual, Interface in Apex post.

• Child extends the Parent class. It means that Parent is a supertype/superclass for Child . Because of this, the following syntax: Parent parent = new Child(); is valid.
• Casting a subclass ( Child ) to a supertype/superclass ( Parent ) is called Upcasting .
• Upcasting can be either explicit or implicit.

Implicit Upcasting

Upcasting can be done implicitly.

Explicit Upcasting

Code should be as simple as possible (KISS rule), so the better approach is to use implicit upcasting.

The parent variable has access to:

• Parent public variables.
• Parent public methods.
• Child ONLY overriden methods.

Downcasting

• Casting a supertype/superclass ( Parent ) to a subclass ( Child ) is called Downcasting .
• Upcasting can be done ONLY explicitly.

Implicit Downcasting

Downcasting CANNOT be implicit. Why?

• There can be many children of the Parent class. e.g public class Child2 extends Parent { ... } .
• Apex needs to know to what type the variable should be cast to.

Explicit Downcasting

You have to cast explicitly (Child) so the compiler checks in the background if this type of casting is possible or not. If not, you will get System.TypeException: Invalid conversion from runtime type Parent to Child .

The child variable has access to:

• Child ALL public methods and variables.
• SObject Class

SObject is a supertype for:

• all standard objects (Account, Contact, etc.)
• all custom objects (MyCustomObject__c)

Object is a supertype for:

• all standard objects
• all custom objects
• all apex classes
• all collections (List, Set and Map)
• all apex types (Integer, String, Boolean)
• Methods inherited from Object class

SObject and Object

Sobject and object - instanceof.

• SObject is an instance of Object . Object is a supertype for SObject .

SObject and Object - casting

Object to sobject.

• Object needs to be explicitly cast to SObject .
• Object is a supertype of SObject .
• Conversion from Object to SObject is called Downcasting .
• As you already know from Downcasting section. Downcasting needs to be explicit (SObject) .

SObject to Object

• SObject can be explicitly or implicitly cast to Object .
• Conversion from SObject to Object is called Upcasting .
• As you already know from Upcasting section. Upcasting can be done explicitly or implicitly.

Inherited methods

• Interestingly, Object is a supertype for SObject , but SObject does NOT inherit Object methods like toString(), equals(), hashCode(), clone() . SObject has all of the following methods SObject class methods. .

However, all Apex Classes inherit Object methods ( toString() , equals() , hashCode() , clone() ).

Standard/Custom Object

Standard/custom object - instanceof.

• Standard/Custom Object is an instance of SObject and Object .
• SObject and Object are supertypes for Standard/Custom Objects .

Standard/Custom Object to SObject - casting

Standard/custom object to sobject.

Why it works?

• SObject is a supertype for Account , Contact , and other standard or custom objects.
• Conversion from Standard/Custom Object to SObject is called Upcasting .

SObject to Standard/Custom Object

• Conversion SObject to Standard/Custom Object is called Downcasting .
• As you already know from Downcasting section. Downcasting can be done ONLY explicitly.

Standard/Custom Object to Object - casting

Standard/custom object to object.

• Object is a supertype for Account , Contact , and other standard or custom objects.
• Conversion from Standard/Custom Object to Object is called Upcasting .

Object to Standard/Custom Object

• Conversion Object to Standard/Custom Object is called Downcasting .

Primitive Types

Primitive types - instanceof.

• All Primitive Data Types are instanceOf Object class.
• Object is a supertype for all primitve types.

Primitive Types - casting

• Primitive Types can be implicilty cast to Object .
• Object is a supertype of all Primitive Types.
• Conversion from Primitive Type to Object is called Upcasting .

List<SObject>

List<sobject> - instanceof.

• List<SObject> is an instance of concrete Standard/Custom Object!
• List<SObject> is NOT an instance of List<Object> .

List<SObject> - casting

List<sobject> to list<object>.

• List<SObject> is NOT an instance of List<Object> (based on instanceOf ), but you can still assign List<SObject> to List<Object> . Do not trust instanceOf !

List<Standard/Custom> to List<SObject>

• List<SObject> is a supertype for List<Standard/Custom> .
• Conversion from Standard/Custom Object to List<SObject> is called Upcasting .

List<SObject> to List<Standard/Custom>

Upcasting/Downcasting (?)

• List<Standard/CustomObject> is an instance of List<SObject> , and List<SObject> is an instance of List<Standard/CustomObject> .
• List<Standard/CustomObject> is a supertype for List<SObject> , and List<SObject> is a supertype for List<Standard/CustomObject> .
• You can do implicit casting.

List<Object>

List<object> - instanceof.

• SObject is always an instance of Object , hovever List<SObject> is NOT an instance of List<Object> .

List<Object> - casting

• We can cast List<ConcreteType> to List<Object> ,
• List<Object> is a supertype of List<ConcreteType> .
• Conversion from List<ConcreteType> to List<Object> is called Upcasting .
• There is no need to cast explicitly by adding (List<Object>) .
• List<SObject> is NOT an instance of List<Object> (based on instanceOf ), but you can still assign List<SObject> to List<Object> .

List Summary

List casting in Apex is a bit unusual.

What is common:

• List<ConcreteType> is an instance of List<Object> .
• List<Object> is a supertype for List<ConcreteType> .

What is unexpected:

• Based on instanceOf . List<SObject> is not an instance of List<Object> , but you can still assign List<SObject> to List<Object> .
• You can even assign List<SObject> to List<Object> . Do not trust instanceOf !
• Even more unexpectedly, List<SObject> is an instance of concrete List<Standard/Custom> Object!

Set<SObject>

Set<sobject> - instanceof.

• Set<Standard/CustomObject> is NOT an instance of Set<SObject> .

Set<SObject> - casting

Set<sobject> to set<object>.

• You CANNOT cast Set<SObject> to Set<Object>

Set<Standard/Custom> to Set<SObject>

• You CANNOT cast Set<Standard/Custom> to Set<SObject>

Set<SObject> to Set<Standard/Custom>

• You CANNOT cast Set<SObject> to Set<Standard/Custom>

Set<Object>

Set<object> - instanceof.

• Other than List , Set<Object> is NOT a supertype for Set<ConcreteType> .

Set<Object> - casting

• We CANNOT cast Set<ConcreteType> to Set<Object> ,

Even if you explicitly add casting (Set<Object>) it will not work.

Set Summary

Map<sobject>, map<sobject> - instanceof.

I skipped cases where SObject is a key. SObject should never be a key in the Map.

• Map<Object, Account> is an instance of Map<Object, Object> , which means that Map<Object, Object> is a supertype of Map<Object, Account> .
• Map<Object, Account> is an instance of Map<Object, SObject> , which means that Map<Object, SObject> is a supertype of Map<Object, Account> .

Map<SObject> - casting

• Map<Object, Object> is a supertype for Map<Object, Standard/CustomObject> .
• Conversion from Map<Object, Standard/CustomObject> to Map<Object, Object> is called Upcasting .

Even explicit casting will not work. The error is different.

How to fix Map downasting?

Map<Object>

Map<object> - instanceof.

Maps are the same instance only in the following cases:

• new Map<MyType, MyType>() instanceOf new Map<MyType, Object>
• new Map<Object, MyType>() instanceOf new Map<Object, Object>

Key Type must be the same.

Map<Object> - casting

You can cast implicitly only when:

Map Summary

Starting from Summer 23', Set implements Iterable interface as List does.

Iterable List

Iterable list - instanceof.

Not surprisingly, a List of concrete types is also an instance of Iterable<Object> .

• Instance of List<Object> and Set<Object> are always an instance of System.Iterable<Object> .

Iterable List - casting

It's really interesting.

e.g List<String> is an instance of Iterable<Object> , but you CANNOT use Iterable<Object> as a supertype .

You need to assign List<String> to List<Object> and after it to Iterable<Object> .

Iterable Set

Iterable set - instanceof.

• An interesting thing is that you're getting an error Operation instanceOf is always true... .
• Set<ConcreteType> is also an instance of Iterable<Object> , but not Set<SObject> .

Iterable Set - casting

• You CAN use Iterable<Object> as a supertype for Set , which you CANNOT do with a List .
• You CANNOT assign Set<SObject> to Iterable<Object> .

It's quite a big deal. Let's check an example:

How to fix it?

• You need two methods ( isIn(Iterable<Object> inList) and isIn(List<Object> inList) ) in the interface that will be covered by one method ( isIn(Iterable<Object> inList) in concrete class!

Iterable Summary

• You CANNOT use Iterable<Object> as a supertype for List<ConcreteType> . You need to assign List<ConcreteType> to List<Object> and after it to Iterable<Object> .
• Set<ConcreteType> is instance of Iterable<Object> .
• Set<Sobject> is NOT instance of Set<SObject> .

Casting Rules

Cast to everything.

The problem with the solution below is performance.

Casting Cheat Sheet

Do not trust instanceof.

Based on the type system is broken with regards to collections :

Pretty much the entire "Type" system that governs Maps, Sets, and Lists is broken. Do not trust instanceOf, use your own logical assessment to determine if something is safe or not.

As shown in the post, there are cases where instanceOf does not work correctly.

List<SObject> and List<Object>

instanceOf says that " List<SObject> is never an instance of List<Object> ", but you can assign List<SObject> to List<Object> .

List<ConcreteType> and Iterable<Object>

instanceOf says that List<ConcreteType> is an instance of Iterable<Object> , but you CANOT assign List<ConcreteType> to Iterable<Object> .

SObject Casting

• Casting from Standard/Custom Object to SObject is called upcasting and can be implicitly.
• Casting from SObject to Standard/Custom Object is called downcasting and it needs to be explicit.
• SObject is instance of Object . Object is a supertype for SObject .
• Casting from SObject to Object is called upcasting and can be implicit.
• Casting from Object to SObject is called downcasting and it needs to be explicit.

Object Casting

Primitive types casting.

• All Primitive Data Types are instanceOf Object . Object is a supertype for all primitve types.
• Casting from Primitive Data Types to Object is called upcasting and can be implicit.

List Casting

• All List<ConcreteType> are instance of List<Object> . List<Object> is a supertype of List<ConcreteType> .
• Based on instanceOf method List<SObject> is NOT an instance of List<Object> , but still you can assign List<SObject> to List<Object> . Do not trust instanceOf .
• Casting from List<ConcreteType> to List<Object> is called upcasting and can be implicit.
• List<Standard/Custom> is a supertype for List<SObject> .

Set Casting

• You CANNOT cast Set<ConcreteType> to Set<Object> .

Map Casting

• Map<Object, Account> is instance of Map<Object, Object> , it means that Map<Object, Object> is a supertype for Map<Object, Account> .
• Map<Object, Account> is instance of Map<Object, SObject> , it means that Map<Object, SObject> is a supertype for Map<Object, Account> .
• To fix System.TypeException: Invalid conversion from runtime type Map<ANY,SObject> to Map<ANY,Account> dynamic Map initiation is needed.

Iterable Casting

• Set<ConcreteType> is instance of Iterable<Object> , but Set<SObject> is NOT instance of Iterable<SObject> .
• Unexpected Iterable behavior in Apex
• Classes and Casting
• Using the instanceOf Keyword
• Upcasting Vs Downcasting in Java

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