append to variable in couchdb rewrite rule

问题

I am trying to create a rewrite rule, to read a view with keys that start with a string.

I can do this without the rewrite, but am struggling to do it with the rewrite.

Access with direct query.

curl -g -H "Accept: application/json" \
    'http://127.0.0.3:80/bookmarks/_design/design/_view/webmarks-by-url?include_docs=true&reduce=false&startkey=["www.sciencemuseum.org.uk"]&endkey=["www.sciencemuseum.org.uk/\ufff0"]' | json_pp

Then I try to do it with a rewrites.json

{
    "from": "bookmarks_by_url/:~name:",
    "to": "_view/webmarks-by-url",
    "query": {
        "reduce": "false",
        "include_docs": "true",
        "descending" : "false",
        "startkey": [":~name:"],
        "endkey": [":~name:\ufff0"]
    }       
},

What I want, but this is obviously not going to work. Is there a way to say this is the end of a variable? Or another way to write the rule?

{
    "from": "bookmarks_by_url/:~name:",
    "to": "_view/webmarks-by-url",
    "query": {
        "reduce": "false",
        "include_docs": "true",
        "descending" : "false",
        "startkey": [":~name:"],
        "endkey": [":~name:" + "\ufff0"]
    }       
},

---

The documentation for rewrite rules are terrible, If you know of better ones then please link.

回答1:

If you are using Couch 2.1+, you may employ JS rewrites to use plain JS function for request routing.

Having .rewrites section, containing a string representation of a router function, you can handle very complex routing. Moreover, you can even serve a response directly from rewrite function.

However, using JS rewrites you also have all JS query server penalties. They are:

• You add several ms to each request latency.
• Your rewrite fn is a single-threaded bottleneck, you can’t handle more requests than your rewrite fn is able to process.
• Since each JS engine instance in Couch has only 64Mb RAM for both compiled code and data, you can’t process large POST requests.
• All QS functions in Couch are hard to debug, rewrite is not an exception.
• You can’t use both old array syntax (which is waaay faster), and a function in one design doc.

Since I personally employ JS rewrite heavily, I can say pros are much heavier than cons. There is an article with some perf details related to JS rewrites.

来源：https://stackoverflow.com/questions/48978344/append-to-variable-in-couchdb-rewrite-rule