如果字段不存在则更新文档

Question

我在mongodb中有两个集合：ColA，ColB。

在colA：

    "_id" : "89479574905"
    "NETWORK" : "AAA",
    "BUSINESS_ID" : "148013"

在colB：

 "_id" : "78787878"
"NETWORK" : "BBB",
"BUSINESS_ID" : "148456",
"BUSINESS_NAME" : "Hello",
"BUSINESS_URL" : "www.some.net",
"LOCATION" : "Delhi"

我想更新colA，以便结果应为：

"_id" : "89479574905"
"NETWORK" : "AAA",
"BUSINESS_ID" : "148013",
"BUSINESS_NAME" : "Hello",
"BUSINESS_URL" : "www.some.net",
"LOCATION" : "Delhi"

如果colA中出现相同的字段，则不要仅更新插入其他字段。

你会怎么做？