Let me start with structure first:
[main_node]->field_reference_to_sub_node->[sub_node]->field_ref_to_sub_sub_node->[sub_sub_node]
[sub_sub_node]->field_type = ['wrong_type', 'right_type']
How to efficiently query all [sub_sub_node] ids with right_type, referenced by main_node (which is current opened node)?
Doing node_load on foreach seems a bit of overkill for this. Anybody has some better solutions? Greatly appreciated!
If you want to directly query the table of the fields:
$query = db_select('node', 'n')->fields('n_sub_subnode', array('nid'));
$query->innerJoin('table_for_field_reference_to_sub_node', 'subnode', "n.nid = subnode.entity_id AND subnode.entity_type='node'");
$query->innerJoin('node', 'n_subnode', 'subnode.subnode_target_id = n_subnode.nid');
$query->innerJoin('table_for_field_ref_to_sub_sub_node', 'sub_subnode', "n_subnode.nid = sub_subnode.entity_id AND sub_subnode.entity_type='node'");
$query->innerJoin('node', 'n_sub_subnode', 'sub_subnode.sub_subnode_target_id = n_sub_subnode.nid');
$query->innerJoin('table_for_field_type', 'field_type', "n_sub_subnode.nid = field_type.entity_id AND field_type.entity_type='node'");
$query->condition('n.nid', 'your_main_node_nid');
$query->condition('field_type.field_type_value', 'right_type');
Here is the explanation of each line:
$query = db_select('node', 'n')->fields('n_sub_subnode', array('nid'));
We start by querying the base node table, with the alias 'n'. This is the table used for the 'main_node'. The node ids which will be returned will be however from another alias (n_sub_subnode), you will see it below.
$query->innerJoin('table_for_field_reference_to_sub_node', 'subnode', "n.nid = subnode.entity_id AND subnode.entity_type='node'");
The first join is with the table of the field_reference_to_sub_node field, so you have to replace this with the actual name of the table. This is how we will get the references to the subnodes.
$query->innerJoin('node', 'n_subnode', 'subnode.subnode_target_id = n_subnode.nid');
A join back to the node table for the subnodes. You have to replace the 'subnode_target_id' with the actual field for the target id from the field_reference_to_sub_node table. The main purpose of this join is to make sure there are valid nodes in the subnode field.
$query->innerJoin('table_for_field_ref_to_sub_sub_node', 'sub_subnode', "n_subnode.nid = sub_subnode.entity_id AND sub_subnode.entity_type='node'");
The join to the table that contains references to the sub_sub_node, so you have to replace the 'table_for_field_ref_to_sub_sub_node' with the actual name of the table. This is how we get the references to the sub_sub_nodes.
$query->innerJoin('node', 'n_sub_subnode', 'sub_subnode.sub_subnode_target_id = n_sub_subnode.nid');
The join back to the node table for the sub_sub_nodes, to make sure we have valid references. You have to replace the 'sub_subnode_target_id' with the actual field for the target id from the 'field_ref_to_sub_sub_node' table.
$query->innerJoin('table_for_field_type', 'field_type', "n_sub_subnode.nid = field_type.entity_id AND field_type.entity_type='node'");
And we can now finally join the table with the field_type information. You have to replace the 'table_for_field_type' with the actual name of the table.
$query->condition('n.nid', 'your_main_node_nid');
You can put now a condition for the main node id if you want.
$query->condition('field_type.field_type_value', 'right_type');
And the condition for the field type. You have to replace the 'field_type_value' with the actual name of the table field for the value.
Of course, if you are really sure that you always have valid references, you can skip the joins to the node table and directly join the field tables using the target id and the entity_id fields (basically the target_id from on field table has to be the entity_id for the next one).
I really hope I do not have typos, so please check the queries carefully.