indexing

问题 I have a collection of documents in MongoDB that looks like: {"_id": 1, "array": [{"id": 1, "content": "..."}, {"id": 2, "content": "..."}]} {"_id": 2, "array": [{"id": 1, "content": "..."}, {"id": 2, "content": "..."}, {"a_id": 3, "content": "..."}]} and I want to ensure that there is no duplicate array.id within each document. So the provided example is ok, but the followign is not: {"_id": 1, "array": [{"id": 1, "content": "..."}, {"id": 1, "content": "..."}]} My question is how to do this

问题 Given a tuple of tuples T : (('a', 'b')) and an individual tuple t1 : ('a','b') why does: t1 in T return False? UPDATE: From Ipython: In [22]: T = (('a','b')) In [23]: t1 = ('a','b') In [24]: t1 in T Out[24]: False And how then to check that a tuple is in another tuple? 回答1: The problem is because T is not a tuple of tuples, it is just a tuple. The comma makes a tuple, not the parentheses. Should be: >>> T = (('a','b'),) >>> t1 = ('a', 'b') >>> t1 in T True In fact, you can loose the outer

问题 Given a tuple of tuples T : (('a', 'b')) and an individual tuple t1 : ('a','b') why does: t1 in T return False? UPDATE: From Ipython: In [22]: T = (('a','b')) In [23]: t1 = ('a','b') In [24]: t1 in T Out[24]: False And how then to check that a tuple is in another tuple? 回答1: The problem is because T is not a tuple of tuples, it is just a tuple. The comma makes a tuple, not the parentheses. Should be: >>> T = (('a','b'),) >>> t1 = ('a', 'b') >>> t1 in T True In fact, you can loose the outer

问题 Is it possible to start the index from n in a pandas dataframe? I have some datasets saved as csv files, and would like to add the column index with the row number starting from where the last row number ended in the previous file. For example, for the first file I'm using the following code which works fine, so I got an output csv file with rows starting at 1 to 1048574, as expected: yellow_jan['index'] = range(1, len(yellow_jan) + 1) I would like to do same for the yellow_feb file, but

问题 I have the following variable: _Data. The variable contains the following info: _Data Variable How can i access the message field? I tried _Data["messages"][0] - but it not wokring. I recieved the following error: Cannot apply indexing with [] to an expression of type 'object' What am i doing wrong? Thanks. 回答1: What am i doing wrong? _Data["messages"] is returning type object . You need to cast it to List<string> or IList<string> in order to use an indexer. var indexable = _Data["messages"]

问题 So I'm experimenting with json column. Mysql 8.0.17 supposed to work with multi value JSON indexes, like this: CREATE INDEX data__nbr_idx ON a1( (CAST(data->'$.nbr' AS UNSIGNED ARRAY)) ) I have column categories with JSON like this ["books", "clothes"]. I need to get all products from "books" category. I can use "json_contains" or new "member of". SELECT * FROM products WHERE JSON_CONTAINS(categories, '\"books\"') SELECT * FROM products WHERE "books" MEMBER OF(categories) And it works. The

问题 So I'm experimenting with json column. Mysql 8.0.17 supposed to work with multi value JSON indexes, like this: CREATE INDEX data__nbr_idx ON a1( (CAST(data->'$.nbr' AS UNSIGNED ARRAY)) ) I have column categories with JSON like this ["books", "clothes"]. I need to get all products from "books" category. I can use "json_contains" or new "member of". SELECT * FROM products WHERE JSON_CONTAINS(categories, '\"books\"') SELECT * FROM products WHERE "books" MEMBER OF(categories) And it works. The

问题 How to create index on sub-documents in Json data type in MySQL server? I know we have to create a generated column from the base table and then need to index that column Virtually or stored. But I want syntax for creating a generated column for sub-document. 回答1: JSON columns, like columns of other binary types, are not indexed directly; instead, you can create an index on a generated column that extracts a scalar value from the JSON column. See Section “Secondary Indexes and Generated

问题 I have such map: Map := make(map[string]interface{}) This map is supposed to contain mapping from string to array of objects. Arrays can be of different types, like []Users or []Hosts . I populated this array: TopologyMap["Users"] = Users_Array TopologyMap["Hosts"] = Hosts_Array but when I try to get an elements from it: Map["Users"][0] it gives an error: (type interface {} does not support indexing) How can I overcome it? 回答1: You have to explicitly convert your interface{} to a slice of the

问题 I am trying out Cloud Datastore's indexes, and I cannot figure out the configuration I need to resolve my queries. I have created a few entities of the same kind (named "object"), all of them with 5 properties named equally (property_0, property_1, ..., property_4). Then, I have created a composite index for that kind, indexing all 5 properties, and setting property_4 in the last place because I want to apply inequality filters on it. The definition of the index is: indexes: - kind: object