CouchDB API

Description

CouchDB NoSQL databases can be queried, updated, and managed using Xbasic. Learn how to perform some of the more common operations on a CouchDB database in this guide to the CouchDB API.

Creating Database 

Couch databases creation is a two step process with the couch object. First you must create the automation object using extension::CouchDB::Create(), then call the CreateDatabase() method.

In the following example, we create an object to reference a couch database called 'people' which does not yet exist, as we can see when we try to get the contents using the GetAllRecords() call.

After calling CreateDatabase(), GetAllRecords() reports that we now have an empty database.

dim cdb as extension::CouchDB = extension::CouchDB::Create("http://127.0.0.1:5984","people")
? cdb.GetAllRecords()
= {"error":"not_found","reason":"no_db_file"}
cdb.CreateDatabase()
? cdb.GetAllRecords()
= {"total_rows":0,"offset":0,"rows":[

]}

Adding Records to a Couch Database 

To add a record to our database, we need to call the AddRecord() with a Json string representing our record.

In the following example we add a record to the people database. You may notice that the record includes an added 'id'.

dim cdb as extension::CouchDB = extension::CouchDB::Create("http://127.0.0.1:5984","people")

dim person as p
dim person.firstname as c = "john"
dim person.lastname as c = "public"
dim person.age as n = 28
cdb.AddRecord(json_generate(person))

= {
    "total_rows": 1,
    "offset": 0,
    "rows": [
        {
            "id": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "key": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "value": {
                "rev": "1-977e69a1ca49f5063fc84267b1569529"
            },
            "doc": {
                "_id": "6c9ae1b840534f24bfd6f4b6cccb891d",
                "_rev": "1-977e69a1ca49f5063fc84267b1569529",
                "firstname": "john",
                "lastname": "public",
                "age": 28,
                "id": "johnpublic"
            }
        }
    ]
}

Updating Existing Records in a Couch Database 

When updating a record, there are two elements you need to identify the record. The id gets passed To the UpdateRecord() method, but this is not enough because couch will only update the record if the revision is also provided.

To demonstrate this issue, I first try and update the record using just the 'id', which will produce an error. Next I look at the contents again, and notice that couch adds a field called '_rev' to the record, and when I copy this value into an _rev field in the record I am updating, the record now updates properly.

dim cdb as extension::CouchDB = extension::CouchDB::Create("http://127.0.0.1:5984","people")

dim person as p
dim person.firstname as c = "John"
dim person.lastname as c = "Public"
dim person.age as n = 29

? cdb.UpdateRecord("6c9ae1b840534f24bfd6f4b6cccb891d",json_generate(person))
= {"error":"conflict","reason":"Document update conflict."}
? json_reformat(cdb.GetAllRecords())
= {
    "total_rows": 1,
    "offset": 0,
    "rows": [
        {
            "id": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "key": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "value": {
                "rev": "1-977e69a1ca49f5063fc84267b1569529"
            },
            "doc": {
                "_id": "6c9ae1b840534f24bfd6f4b6cccb891d",
                "_rev": "1-977e69a1ca49f5063fc84267b1569529",
                "firstname": "john",
                "lastname": "public",
                "age": 28,
                "id": "johnpublic"
            }
        }
    ]
}

dim person._rev as c = "1-977e69a1ca49f5063fc84267b1569529"

? cdb.UpdateRecord("6c9ae1b840534f24bfd6f4b6cccb891d",json_generate(person))
= {"ok":true,"id":"6c9ae1b840534f24bfd6f4b6cccb891d","rev":"2-699c5d916d959211637c5d70bff9c4e6"}
? json_reformat(cdb.GetAllRecords())
= {
    "total_rows": 1,
    "offset": 0,
    "rows": [
        {
            "id": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "key": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "value": {
                "rev": "2-699c5d916d959211637c5d70bff9c4e6"
            },
            "doc": {
                "_id": "6c9ae1b840534f24bfd6f4b6cccb891d",
                "_rev": "2-699c5d916d959211637c5d70bff9c4e6",
                "firstname": "John",
                "lastname": "Public",
                "age": 29
            }
        }
    ]
}

Deleting a Record in a Couch Database 

Deleting a record requires both the id and a revision number just like UpdateRecord. Since delete does not take a Json record to include the revisions, the revision gets passed as a second argument.

dim person._rev as c = "1-977e69a1ca49f5063fc84267b1569529"

? json_reformat(cdb.GetAllRecords())
= {
    "total_rows": 1,
    "offset": 0,
    "rows": [
        {
            "id": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "key": "6c9ae1b840534f24bfd6f4b6cccb891d",
            "value": {
                "rev": "2-699c5d916d959211637c5d70bff9c4e6"
            },
            "doc": {
                "_id": "6c9ae1b840534f24bfd6f4b6cccb891d",
                "_rev": "2-699c5d916d959211637c5d70bff9c4e6",
                "firstname": "John",
                "lastname": "Public",
                "age": 29
            }
        }
    ]
}

cdb.DeleteRecord("6c9ae1b840534f24bfd6f4b6cccb891d","2-699c5d916d959211637c5d70bff9c4e6")
? json_reformat(cdb.GetAllRecords())
= {
    "total_rows": 0,
    "offset": 0,
    "rows": []
}

Performing Queries Against CouchDB 

So far the examples have only shown the GetAllRecords() method, which gets the entire databases to a single Json string, which is not very useful as the databases gets larger. Fortunately there is a very flexible method to control what columns and rows get returned so that you can restrict your search.

A view is defined using javascript map and optional reduce methods that are run on the CouchDB server.

In the following example, there is a database of 'flowers' which is fully populated, as we can see, it has Id, Picture, Imagedate and Keywords.

dim cdb as extension::CouchDB = extension::CouchDB::Create("http://127.0.0.1:5984","flowers")


? json_reformat( cdb.GetAllRecords() )
= {
    "total_rows": 60,
    "offset": 0,
    "rows": [
        {
            "id": "02781af088474adcbb5509fea0e45d20",
            "key": "02781af088474adcbb5509fea0e45d20",
            "value": {
                "rev": "2-86b9bd1c9cc4c871a15264a578dc4434"
            },
            "doc": {
                "_id": "02781af088474adcbb5509fea0e45d20",
                "_rev": "2-86b9bd1c9cc4c871a15264a578dc4434",
                "Id": "00000021",
                "Picture": "=filename_decode(\"Hires\\lily orange.jpg\")",
                "Imagedate": "07/07/2002",
                "Keywords": "lily orange"
            }
        },
 ....

At first we are interested in limiting the columns to just the Id and the Keywords columns, so we define a map subfield with the javascript function(doc) { emit(doc.Id,doc.Keywords); } which gets executed for each record in the databases.

dim view as p
dim view.map as c = "function(doc) { emit(doc.Id,doc.Keywords); }"
? cdb.GetTemporaryView(json_generate(view))
= {"total_rows":60,"offset":0,"rows":[
{"id":"7bc319a61b19439ea4466026fa1ab003","key":"00000000","value":"allium white"},
{"id":"945f9e032fb14c01ae18200c5318b045","key":"00000001","value":"alyssum purple"},
{"id":"1ef7f1edf7f641f38f03c5b959cd9c80","key":"00000002","value":"anenome white"},
{"id":"a3a168b881bd4b50bc2efedfdc6ff114","key":"00000003","value":"anenome white"},
{"id":"3452c8a9e20b487f9bf22e5a341a373f","key":"00000004","value":"white boltonia daisy"},
{"id":"c8c9bf02e4c947de9d4e71fc20630567","key":"00000005","value":"campanula purple"},
{"id":"0f494b1637504652961a659a232cb8c5","key":"00000006","value":"clematis white vine"},
{"id":"d7fa42b4d9d0446e9a7c41a5d757e7fd","key":"00000007","value":"clivia orange indoor"},
....

Next, we only want to return these columns for the records that contain 'lily orange'.

dim view.map as c = "function(doc) { if(doc.Keywords == 'lily orange') emit(doc.Id,doc.Keywords); }"
? cdb.GetTemporaryView(json_generate(view))
= {"total_rows":1,"offset":0,"rows":[
{"id":"02781af088474adcbb5509fea0e45d20","key":"00000021","value":"lily orange"}
]}

Finally, we use the javascript indexOf string function to return all the records whose keyword contains the word 'lily'.

dim view.map as c = "function(doc) { if(doc.Keywords.indexOf('lily') >= 0) emit(doc.Id,doc.Keywords); }"
? cdb.GetTemporaryView(json_generate(view))
= {"total_rows":6,"offset":0,"rows":[
{"id":"a5223e50f84a4804846bec2faaf7ee28","key":"00000020","value":"lily yellow"},
{"id":"02781af088474adcbb5509fea0e45d20","key":"00000021","value":"lily orange"},
{"id":"1652cbd63bf54b85b2719599221805fc","key":"00000039","value":"lily pink"},
{"id":"ec86ae483b20430c9773fb47d8dc973d","key":"00000040","value":"lily pink white"},
{"id":"2ff26fa9e660414d9d84801abf716c4d","key":"00000041","value":"daylily stella doro yellow"},
{"id":"d627f97b78fa49b6bf3ed03ccce9c14f","key":"00000042","value":"lily yellow"}
]}
dim record._id as c = "_design/myQuery"
dim record.language as c = "javascript"
dim record.views as p
dim record.views.all.map as c = "function(doc) { emit(null, doc) }"
dim record.views.id_and_keyword.map as c = "function(doc) {  emit(doc.Id, doc.Keywords) }"
cdb.AddRecord(json_generate(record))

See Also