Question

我有一个临时列和最小临时列。 temp列刚刚连续写入，但是当temp小于minTemp时，minTemp会更新以反映新的低值。我知道下面的代码是错误的，所以我的专栏是

id and date <- these are my keys
temp <- this is the current temperature
minTemp <- this is the lowest temperature for the day

这是非工作代码，但要了解我想要做什么

var tparams = {
    Key: { id: id, date: dayofyear(date)},
    TableName: "myTable",
    UpdateExpression: "Set minTemp = temp",
    ConditionExpression: "temp < minTemp",

    ExpressionAttributeValues:{
    'temp' : 'minTemp
      }
    ReturnValues: "UPDATED_NEW" 
  };
console.log(tparams);

为什么aws文档似乎没有什么帮助呢？

Answer 1

这是适合我的解决方案。虽然

可能有更好的方法

attrNamesMinT["#minTemp"] = "minTemp";
attValuesMinT[":mint"] = temperature;

var mintparams = {
    TableName: "myTable",
    Key: { id: id, date: dayofyear(date)},
    UpdateExpression: "Set #minTemp = :mint",
    ConditionExpression: ":mint < #minTemp  or attribute_not_exists(#minTemp)",
    ExpressionAttributeNames: attrNamesMinT,
    ExpressionAttributeValues: attValuesMinT,
    ReturnValues: "UPDATED_NEW"
};


console.log(mintparams);
dynamo.updateItem(mintparams, function(err,res){
    console.log(err);
});

比DynamoDB条件更新更大/更小的适当格式

1 个答案: