使用 SQLAlchemy 按匹配的标签排序

Question

I have following tables. I want to search by tags, and sort by matched number of tags.

class DocumentTag(db.Model):
    __tablename__ = "document_tag"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50), nullable=False)
    user_document_id = db.Column(db.Integer, db.ForeignKey("user_document.id"))
    order = db.Column(db.Integer, nullable=False)

    user_document = db.relationship("Document")

class UserDocument(db.Model):
    __tablename__ = "user_document"
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer, db.ForeignKey("user.id"), nullable=False)
    document_id = db.Column(db.Integer, db.ForeignKey("document.id"), nullable=False)
    date_added = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    last_accessed = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    document_tags = db.relationship(
        "DocumentTag",
        order_by="DocumentTag.order",
        collection_class=ordering_list("order"),
    )
    document = db.relationship("Document")
    document_tag = db.relationship("DocumentTag")

I tried to search documents with tags like this.

tags = ['tag_1', 'tag_2'] # this is tags to search

documents_tags_count = (
    db.session.query(
        UserDocument, func.count(DocumentTag.id).label("num_corres_tags")
    )
    .join(UserDocument, DocumentTag.user_document) # in order to count combination of document_tags and tags
    .filter(
        UserDocument.document_tags.any(DocumentTag.name.in_(tags)),
        UserDocument.user_id == current_user.id,
    )
    .group_by(UserDocument)
    .order_by(desc("num_corres_tags"))
)

However, the label num_corres_tags showed not filtered number of tags but all number of tags which belongs to the documents. What I wanted to do was get ordered result by number of matched (filtered) tags.

I saw some similar questions for MySQL here, but I couldn't find any solution for SQLAlchemy because I'm really new to the SQL.

Is there any ideas to solve my problem?

Answer 1

Since you explicitly join DocumentTag in order to count, use that join to do the filtering as well instead of using an EXISTS subquery expression separately:

documents_tags_count = (
    db.session.query(
        UserDocument, func.count(DocumentTag.id).label("num_corres_tags")
    )
    .join(UserDocument, DocumentTag.user_document) # in order to count combination of document_tags and tags
    .filter(
        DocumentTag.name.in_(tags),
        UserDocument.user_id == current_user.id,
    )
    .group_by(UserDocument)
    .order_by(desc("num_corres_tags"))
)

Now the results are limited to matching tags only and the count should be what you expected.