CDS Filtering based on relationships

[chydewf1]

I have 3 entities in the CDS.

1. Material Table

 Containing the following columns:

Cost

Material Name

Material ID

Min size

modulus

2. Machine Table

Containing the following columns:

X size

Y size

Z size

Machine Name

Machine ID

Purchase date

3. Material Machine Map

With many to one relationships back to the machine table and material table

The data in this table matches machines to materials ie several materials can be used with each machine.

What I want to do is filter a table of materials but a chosen machine.

ie have a drop down to choose one of the machines which then filters a table showing which materials are matched up to that machine. 

I'm not sure if i'm using the CDS correctly or if i'm just getting the filter formula wrong but i'm struggling to get it to work correctly.

Thanks

Chris