toy example for getting sample tracking going at CHX

sample_example.py

# Do this part whether you acquiring data or accessing it.                      
import pymongo         
cli = pymongo.MongoClient('xf11id-ca')    
samples = cli.get_database('samples').get_collection('samples')                 
from databroker import Broker                                                   
db = Broker.named('temp')  # for real applications, 'temp' would be 'chx'       
                                                                                
                                                                                
# Do this part when you are entering new samples.                               
# I'm going to assume that 'name' is unique. We should be more careful about    
# ensuring that and maybe come up with a richer system, but this is good enough 
# for a toy exmaple.                                                            
samples.insert(dict(name='A', composition='Ni'))                                
samples.insert(dict(name='B', composition='Au'))                                
                                                                                
                                                                                
# Here I import something things and set up RE to send documents to db, as the  
# IPython profile (profile_collection) does, so that data acquisition works.    
from bluesky import RunEngine                                                   
RE = RunEngine({})                                                              
from ophyd.sim import det                                                       
from bluesky.plans import count                                                 
RE.subscribe(db.insert)                                                         
                                                                                
                                                                                
# Take some simulated data.                                                     
RE(count([det]), sample='A', purpose='dan is testing for Lutz')                 
                                                                                
                                                                                
# This is the part you have to add to make data access work.                    
def fetch_sample(start, stop):                                                  
    if 'sample' in start:                                                       
        query = dict(name=start['sample'])                                      
        return samples.find_one(query)                                          
# This tells the databroker to addd some custom stuff to the `.ext` attribute   
# of each Header.                                                               
db.external_fetchers['sample_info'] = fetch_sample                              
print(db[-1].ext.sample_info)