Playa Coparents: Getting just the matrix row I want

Question

This is what I want to do: Show data just from a Matrix row whose Playa column is the child that 2 channels (coparents) share.

I have 3 channels: Sizes, Colors, and Price Groups. Sizes has a playa field "cf_price_group_playa" which references Price Group, and Colors has a Matrix field, cf_size_price, with a playa column, that references the channel Price Group as well. I want to pull only the price for this size in the price group that the color I'm currently looking at is in; if I don't search explicitly on that playa column, I get all the matrix rows:

{exp:channel:entries channel="colors"}
    {exp:playa:coparents channel="sizes"  field="cf_price_group_playa"} 
        {cf_size_price search:price_group="THE_SHARED_PRICE_GROUP"}
        {price}
        {/cf_size_price}
    {/exp:playa:coparents}
{/exp:channel:entries} 

I'm clearly doing something wrong and am tripping myself up figuring it out. It seems so clear, the relationship among these channels, but I'm not getting the front-end bit right. I appreciate insight from the Playa gurus here!

Answer 1

got it! it's all in the var_prefix'ing, on both the playa field AND the playa parents field:

{exp:channel:entries channel="colors"}
    {cf_color_price_group_playa var_prefix="group"}   
        {exp:playa:parents channel="sizes" entry_id="{group:entry_id}" var_prefix="size"} 
         {size:cf_size_price search:price_group="{group:entry_id}"}{size:price}{/size:cf_size_price} 
        {/exp:playa:parents}
    {/cf_color_price_group_playa}
{/exp:channel:entries}

this post helped immensely, thanks rob + jason, Playa Parents entry_id using child ids