run = (relations, target, fk) => {
            _.each(relations, (relation) => {
                if (!relation.post_id) {
                    return;
                }

                let postToImport = _.find(this.dataToImport, {id: relation.post_id});

                // CASE: we won't import a relation when the target post does not exist
                if (!postToImport) {
                    return;
                }

                if (!postToImport[target] || !_.isArray(postToImport[target])) {
                    postToImport[target] = [];
                }

                // CASE: detect duplicate relations
                if (!_.find(postToImport[target], {id: relation[fk]})) {
                    postToImport[target].push({
                        id: relation[fk]
                    });
                }
            });
        }
from {post_id: 1, tag_id: 2} to post.tags=[{id:id}]
from {post_id: 1, author_id: 2} post.authors=[{id:id}]
from {post_id: 1, product_id: 2} post.products=[{id:id}]