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March 11, 2020 09:51
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Shows how we can choose to only update documents with older values of our property using timestamps
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/** create connection pool to system DB in MongoDB | |
* assume we are using https://www.npmjs.com/package/mongodb | |
* assume we begin with: | |
{ | |
system_id: 123, | |
a: 1, | |
b: 2, | |
c: 3, | |
last_modified: { | |
a: '2020-03-10T10:33:13.012Z' | |
} | |
} | |
Receive new state with the following data: | |
{ | |
system_id: 123, | |
a: 4, | |
published: '2020-03-10T10:33:43.012Z' | |
} | |
*/ | |
system_states_collection.update( | |
// find document with timestamp for 'a' less than or equal to our timestamp | |
{ system_id: 123, 'last.modified.a': { $lte: Date('2020-03-10T10:33:43.012Z') }, | |
{ | |
$set: { | |
a: 4, | |
'last_modified.a': Date('2020-03-10T10:33:43.012Z') | |
}, | |
} | |
) | |
/** | |
* Document will only be updated if it finds a document with a | |
* value for property 'last_modified.a' less than or equal to our | |
* timestamp (which is the published time of the update from our source) | |
*/ | |
/** | |
Resulting document: | |
{ | |
system_id: 123, | |
a: 4, | |
b: 2, | |
c: 3, | |
last_modified: { | |
a: '2020-03-10T10:33:43.012Z' | |
} | |
} | |
*/ |
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