Why Does JSON Break SObject Equality with Decimals?

Question

Why Does JSON Roundtrip Deserialization Break SObject Equality for Decimals in Apex?

I’ve noticed an issue where SObject equality is broken after a JSON roundtrip when the SObject contains Decimal fields. Here’s an example:

Opportunity o1 = new Opportunity(Amount = 12.3);
Opportunity o2 = (Opportunity) JSON.deserialize(JSON.serialize(o1), Opportunity.class);
System.debug(o1 == o2); // Outputs: false

However, when the SObject does not contain Decimal fields, the equality remains intact:

Opportunity o3 = new Opportunity(Name = 'foo');
Opportunity o4 = (Opportunity) JSON.deserialize(JSON.serialize(o3), Opportunity.class);
System.debug(o3 == o4); // Outputs: true

My Questions:

1. Why does the equality contract break specifically for Decimal fields during a JSON serialization/deserialization roundtrip?
2. Is there a way to prevent this behavior or ensure that equality is maintained for SObjects with Decimal fields after deserialization?

Keywords: Apex, JSON, SObject, Decimal, Equality, Serialization, Deserialization

Answer

When working with SObjects in Salesforce, you may encounter a situation where serializing and deserializing an SObject containing Decimal fields breaks the equality contract (==). Consider the following example:

Opportunity o1 = new Opportunity(Amount = 12.3);
Opportunity o2 = (Opportunity) JSON.deserialize(JSON.serialize(o1), Opportunity.class);
System.debug(o1 == o2); // false

In this scenario, even though System.debug(o1.Amount) and System.debug(o2.Amount) output the same value (12.3), the equality check o1 == o2 returns false. However, for SObjects without Decimal fields, equality is preserved during the roundtrip:

Opportunity o3 = new Opportunity(Name = 'foo');
Opportunity o4 = (Opportunity) JSON.deserialize(JSON.serialize(o3), Opportunity.class);
System.debug(o3 == o4); // true

This discrepancy arises because of how Decimal fields are handled during JSON serialization and deserialization. The Decimal field may lose certain metadata or precision, leading to inequality when the == operator compares the two SObjects.

To resolve this issue and restore equality, you can explicitly cast the Decimal field back to its original data type after deserialization. For example:

Opportunity o1 = new Opportunity(Amount = 12.3);
Opportunity o2 = (Opportunity) JSON.deserialize(JSON.serialize(o1), Opportunity.class);

System.debug(o1.Amount); // 12.3
System.debug(o2.Amount); // 12.3
System.debug(o1 == o2); // false

o2.Amount = (Decimal) o2.Amount;
System.debug(o1 == o2); // true

By explicitly casting o2.Amount to Decimal, you ensure that the field’s data type is consistent and that the equality check will succeed.

Alternative Approach

If modifying the deserialized object directly is not feasible or desirable, you can implement a custom equality check that compares individual field values instead of relying on the == operator. For example:

public static Boolean areOpportunitiesEqual(Opportunity o1, Opportunity o2) {
    return o1.Amount == o2.Amount && o1.Name == o2.Name;
}

Opportunity o1 = new Opportunity(Amount = 12.3, Name = 'Deal A');
Opportunity o2 = (Opportunity) JSON.deserialize(JSON.serialize(o1), Opportunity.class);

System.debug(areOpportunitiesEqual(o1, o2)); // true

This approach provides more control over how equality is determined and avoids relying on the default behavior of the == operator.

Summary

When an SObject with Decimal fields undergoes JSON serialization and deserialization in Salesforce, the equality check (==) fails, even though the field values appear identical. This happens because the process may subtly alter the Decimal field’s internal representation.

To resolve this, you can:

Cast the Decimal field back to its original type after deserialization:apexCopy code

o2.Amount = (Decimal) o2.Amount;
System.debug(o1 == o2); // true

Implement a custom equality method to compare individual field values directly:

public static Boolean areOpportunitiesEqual(Opportunity o1, Opportunity o2) {
    return o1.Amount == o2.Amount && o1.Name == o2.Name;
}

Both approaches ensure that the equality check produces the expected results for SObjects.

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