How to create UniqueIndex and nullable string field in doctrine 2?

Question

In a collection I have a string field that can be null some times. But, If that field has a value, it should be unique.I have tried like this,

/** @ODM\Field(type="string", nullable=true) @ODM\UniqueIndex(order="asc") */
private $empId;

I am using mongodb 3.0 ,doctrine 2 ORM on Zend Framework 2

Anyone know something on how to do that or if it's possible ?

Check the answer here: https://stackoverflow.com/a/9693138/1697459 — Wilt, Jun 07 '17 at 13:37
@Wilt, yes!, I got a answer from above, need to use 'sparse' option. — sasitha999, Jun 10 '17 at 16:33

score 1 · Accepted Answer · answered Jun 10 '17 at 17:01

Using mongodb sparse option, I can achieve above scenario.

/** @ODM\Field(type="string" ) @ODM\UniqueIndex(sparse=true) */
private $empId;

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