Duplicate entries in view with node to node relationships

Issue #1506524: Duplicate entries in view with node->node relation was duplicate to this. I also tested this and noticed that with just one relation the duplication won't occur.

On #1506524: Duplicate entries in view with node->node relation I pointed out the important differences between the two sql queries one using the views relationship node->node and the other using two relationships 1:node->relation and 2:relation->node (which is somehow also a node-to-node relationship). Using the first two relationships, I set Position of the relationship base for the first to source and for second to target. For the node->node I only can set source, there is no second option to set the joined node to target. I guess this results in the difference between the two ways to get a node-to-node relationship, one with and the other one without duplicates.

I ran into this issue of duplicates appearing in views on a site with one node=>node relation. I did as was suggested in number #3 and was able to remedy this, but it does make the setup less intuitive. I do not think this was an issue until the last update of relation.

i am having the same issue. "require relationship fixes" it but then you are not able to see what node has NO relationship (for example to check who forgot to add one).

I think the query that results when an optional node -> node relation is used is wrong:

SELECT node_node.title AS node_node_title, node_node.nid AS node_node_nid, node.title AS node_title, node.created AS node_created
FROM
{node} node
LEFT JOIN {field_data_endpoints} field_data_endpoints ON node.nid = field_data_endpoints.endpoints_entity_id AND (field_data_endpoints.bundle = 'articles' AND field_data_endpoints.endpoints_entity_type = 'node' AND field_data_endpoints.endpoints_r_index = '0')
LEFT JOIN {field_data_endpoints} field_data_endpoints2 ON field_data_endpoints.entity_id = field_data_endpoints2.entity_id AND field_data_endpoints2.endpoints_entity_type = 'node'
LEFT JOIN {node} node_node ON field_data_endpoints2.endpoints_entity_id = node_node.nid AND (field_data_endpoints2.endpoints_r_index != field_data_endpoints.endpoints_r_index AND 1 = '1' AND field_data_endpoints2.endpoints_entity_type = 'node')
WHERE (( (node.status = '1') AND (node.type IN ('page')) AND (node.nid = '8') ))
ORDER BY node_created DESC
LIMIT 10

I think it should be:

SELECT node_node.title AS node_node_title, node_node.nid AS node_node_nid, node.title AS node_title, node.created AS node_created
FROM
{node} node
LEFT JOIN {field_data_endpoints} field_data_endpoints ON node.nid = field_data_endpoints.endpoints_entity_id AND (field_data_endpoints.bundle = 'articles' AND field_data_endpoints.endpoints_entity_type = 'node' AND field_data_endpoints.endpoints_r_index = '0')
LEFT JOIN {field_data_endpoints} field_data_endpoints2 ON field_data_endpoints.entity_id = field_data_endpoints2.entity_id AND (field_data_endpoints2.endpoints_entity_type = 'node' AND field_data_endpoints2.endpoints_r_index != field_data_endpoints.endpoints_r_index AND 1 = '1')
LEFT JOIN {node} node_node ON field_data_endpoints2.endpoints_entity_id = node_node.nid AND field_data_endpoints2.endpoints_entity_type = 'node'
WHERE (( (node.status = '1') AND (node.type IN ('page')) AND (node.nid = '8') ))
ORDER BY node_created DESC
LIMIT 10

Attached patch achieves this. It also adds a left/right text to the "Avoid left node duplication" checkbox, although I don't really get its function.

I am interested to hear if it also solves your problems.

In my opinion, the test was expecting erroneous output. In the case that failed, there was a symmetric relation between two entities (A and B). For a non-required relationship, the expected result was two rows, one with (A, B) and one with (A, NULL). I think this behavior is unwanted: the choice between required and non-required should only affect the inclusion of entities that do not have a relationship of that kind. I have improved the tests by also including tests for a node without any relations (node6). I have split the large test method in relation.views.test so debugging test failures becomes easier.

Awesome, thanks for patch.

Thanks for the commit and git attribution.