Conditionals: Use relationship fields within a grid field as variables?

Question

I have a grid field that contains a relationship field. I want to alter the output according to whether or not a particular field in the related entry contains data or not. For instance:

{if grid_field:relationship_field:related_entry_content_field != ""}Do this{if:else}Do something else{/if}

Instead of the expected results, it prints "{if" then seems to evaluate both conditions as true.

Any ideas on how to make this work?

Edit: Here are some examples of what works and what doesn't work:

{exp:channel:entries channel="channel_name" search:search_field="={segment_x}" dynamic="no"}
    {grid_field}
            {!-- Grid field, then relationship field, then field from the related entry - no tag pair. This works: --}
            <h1>{grid_field:relationship_field:title}</h1>
            {!-- Same syntax as above but used in a conditional. Does not work: --}
            <h2>{if grid_field:relationship_field:title == "foo"}Foo{if:else}Not foo{/if}</h2>
            {!-- Using tag pair for the relationship field as suggested below. This works: --}
            {grid_field:relationship_field}
                <h3>{if grid_field:relationship_field:title == "foo"}Foo{if:else}Not foo{/if}</h3>
            {/grid_field:relationship_field}
    {/grid_field}
{/exp:channel:entries}

Here is the output from the above code:

Title of Related Entry (Desired result from Line 4)
{ifFooNot foo (Weird result from Line 6)
Not foo (Desired result from Lines 8 - 10)

Hopefully this helps someone else!

Answer 1

Both Grid and Relationships are tag pairs (as both can have many), so you can't just request the end point without telling EE which end point you want (which row and which relation).

This should work:

{grid_field}
    {grid_field:relationship_field}
        {if grid_field:relationship_field:related_entry_content_field != ""}
            Do this
        {if:else}
            Do something else
        {/if}
    {/grid_field:relationship_field}
{/grid_field}

You might have to replace in the above the if conditional with this:

{if "{grid_field:relationship_field:related_entry_content_field}" != ""}

Edit based on Question Update:

The cause for the broken conditional is the the same - you have to have the relationship pair. You can implement in a single line conditional:

{grid_field}
    {if "{grid_field:relationship_field}{grid_field:relationship_field:related_entry_content_field}{/grid_field:relationship_field}" != ""}
        Do this
    {if:else}
        Do something else
    {/if}
{grid_field}

Obviously this will fail if there are multiple relationships for the same grid row.