programmatic generation of CouchDB views
5 August 2008
23:55
as Python
Some utility classes I'm experimenting with to auto-generate CouchDB views based on criteria.
| 1 | class Query(object): |
|---|---|
| 2 | INEQ = ('<=', '>=') # TODO support < and > |
| 3 | EQ = ('=',) |
| 4 | OPS = INEQ + EQ |
| 5 | |
| 6 | MIN_DEFAULT = None |
| 7 | MAX_DEFAULT = {} |
| 8 | |
| 9 | def __init__(self): |
| 10 | self.preconditions = [] |
| 11 | self.key_props = [None] |
| 12 | self.min_key = [] |
| 13 | self.max_key = [] |
| 14 | |
| 15 | def require(self, precondition): |
| 16 | self.preconditions.append(precondition) |
| 17 | |
| 18 | def filter(self, spec, value): |
| 19 | prop, op = spec.split() |
| 20 | if op == '<=': |
| 21 | if self.key_props[-1] == prop and self.max_key[-1] is Query.MAX_DEFAULT: |
| 22 | self.max_key[-1] = value |
| 23 | else: |
| 24 | self.key_props.append(prop) |
| 25 | self.min_key.append(Query.MIN_DEFAULT) |
| 26 | self.max_key.append(value) |
| 27 | elif op == '>=' : |
| 28 | if self.key_props[-1] == prop and self.min_key[-1] is Query.MIN_DEFAULT: |
| 29 | self.min_key[-1] = value |
| 30 | else: |
| 31 | self.key_props.append(prop) |
| 32 | self.min_key.append(value) |
| 33 | self.max_key.append(Query.MAX_DEFAULT) |
| 34 | elif op == '=': |
| 35 | self.key_props.append(prop) |
| 36 | self.min_key.append(value) |
| 37 | self.max_key.append(value) |
| 38 | return self |
| 39 | |
| 40 | def run(self, db): |
| 41 | return self._run(db)[self.min_key:self.max_key] |
| 42 | |
| 43 | def _run(self, db): |
| 44 | return db.query(self._gen_view()) |
| 45 | |
| 46 | def _gen_view(self): |
| 47 | return ('function(doc) {' |
| 48 | + self._gen_precondition() |
| 49 | + 'emit([' |
| 50 | + ', '.join('doc.' + prop for prop in self.key_props[1:]) |
| 51 | + '], doc); }') |
| 52 | |
| 53 | def _gen_precondition(self): |
| 54 | if not self.preconditions: |
| 55 | return '' |
| 56 | conditions = '&&'.join(('(%s)' % pc) for pc in self.preconditions) |
| 57 | return 'if (!(%s)) return;' % conditions |
| 58 | |
| 59 | |
| 60 | class SchemaQuery(Query): |
| 61 | def __init__(self, type_): |
| 62 | super(SchemaQuery, self).__init__() |
| 63 | self.type = type_ |
| 64 | self.require('doc.type == "%s"' % type_.__name__) |
| 65 | |
| 66 | def _run(self, db): |
| 67 | return self.type.query(db, self._gen_view(), None) |
| 68 | |
| 69 | |
| 70 | class CachedQueryMixin(object): |
| 71 | def store(self, db): |
| 72 | doc = db.get(self._design_doc()) |
| 73 | if doc is None: |
| 74 | doc = {'language': 'javascript', 'views': {}} |
| 75 | doc['views'][self._view_func()] = { |
| 76 | 'language': 'javascript', |
| 77 | 'map': self._gen_view(), |
| 78 | } |
| 79 | db[self._design_doc()] = doc |
| 80 | |
| 81 | def exists_in(self, db): |
| 82 | try: |
| 83 | doc = db[self._design_doc()] |
| 84 | except KeyError: |
| 85 | return False |
| 86 | return self._view_func() in doc['views'] |
| 87 | |
| 88 | def _run(self, db): |
| 89 | return db.view(self._view_doc()) |
| 90 | |
| 91 | def _design_doc(self): |
| 92 | return '_design/' + self._view_ns() |
| 93 | |
| 94 | def _view_doc(self): |
| 95 | return '_view/' + self._view_name() |
| 96 | |
| 97 | def _view_name(self): |
| 98 | return self._view_ns() + '/' + self._view_func() |
| 99 | |
| 100 | def _view_ns(self): |
| 101 | return 'saved_queries' |
| 102 | |
| 103 | def _view_func(self): |
| 104 | if len(self.key_props) == 1: |
| 105 | return 'all' |
| 106 | return 'by_' + '_'.join(self.key_props[1:]) |
| 107 | |
| 108 | |
| 109 | class CachedSchemaQuery(SchemaQuery, CachedQueryMixin): |
| 110 | def _run(self, db): |
| 111 | return self.type.view(db, self._view_doc()) |
| 112 | |
| 113 | def _view_ns(self): |
| 114 | return self.type.__name__ |
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