我很难找到一个有用的示例,用于在dynamodb表上使用filterexpression进行扫描。我正在浏览器中使用JavaScript SDK。
我想扫描我的表格,并仅返回那些在数组中具有哈希字段" uid"值的记录,我将其传递给扫描
可以说我有一系列独特的ID,这些ID是我桌子的哈希字段我想从DynamoDB表中查询这些记录。
类似于下面的东西
var idsToSearch=['123','456','789'] //array of the HASH values I would like to retrieve
var tableToSearch = new AWS.DynamoDB();
var scanParams = {
"TableName":"myAwsTable",
"AttributesToGet":['ID','COMMENTS','DATE'],
"FilterExpression":"'ID' in "+idsToSearch+""
}
tableToSearch.scan(scanParams), function(err,data){
if (err) console.log(err, err.stack); //error handler
else console.log(data); //success response
})
您应该使用IN
操作员。将占位持有人用于属性名称和属性值也更容易。但是,我建议不要在这种情况下使用Scan
。听起来您已经有了要找到的哈希密钥属性值,因此使用BatchGetItem
。
无论如何,这是您在Java中的做法:
ScanSpec scanSpec = new ScanSpec()
.withFilterExpression("#idname in (:val1, :val2, :val3)")
.withNameMap(ImmutableMap.of("#idname", "ID"))
.withValueMap(ImmutableMap.of(":val1", "123", ":val2", "456", ":val23", "789"));
ItemCollection<ScanOutcome> = table.scan(scanSpec);
我想像使用JavaScript SDK,那将是这样的:
var scanParams = {
"TableName":"myAwsTable",
"AttributesToGet": ['ID','COMMENTS','DATE'],
"FilterExpression": '#idname in (:val1, :val2, :val3)',
"ExpressionAttributeNames": {
'#idname': 'ID'
},
"ExpressionAttributeValues": {
':val1': '123',
':val2': '456',
':val3': '789'
}
}
我遇到了这个问题,并使用包含参数
来弄清楚它// Object stored in the DB looks like this:
// [
// 'name' => 'myName',
// 'age' => '24',
// 'gender' => 'Male',
// 'visited' => [
// 'countries': ['Canada', 'USA', 'Japan', 'Australia'],
// 'last_trip': '2015/12/13',
// 'reviews_written': 20
// ]
//
// ];
$countries = ['Canada', 'USA', 'Japan', 'Australia'];
$paramToMatch = '24';
$client->query([
'TableName' => 'MyDyanmoDB',
'KeyConditions' => [
'age' => [
'AttributeValueList' => [
$marshaler->marshalValue($paramToMatch)
],
'ComparisonOperator' => 'EQ'
]
],
'ExpressionAttributeNames' => [
'#visited' => 'visited',
'#countries' => 'countries'
],
'ExpressionAttributeValues' => [
':countries' => $marshaler->marshalValue($countries)
],
'FilterExpression' => 'contains(:countries, #visited.#countries)',
]);
这是我能够使用"扫描"的方式。在下面的示例中获取具有特定ID(contentid; contentid; contentid; quotid')的项目:
var params = {
TableName: environment.ddbContentTableName,
ProjectionExpression: "Title, ContentId, Link",
FilterExpression: "ContentId in (:contentId1, :contentId2, :contentId3, :contentId4)",
ExpressionAttributeValues: {":contentId1":102,":contentId2":104,":contentId3":103,":contentId4":101}
};
var docClient = new AWS.DynamoDB.DocumentClient();
docClient.scan(params, onQuery);
然后,我可以根据已知值例如。 // Create the FilterExpression and ExpressionAttributeValues
var filterExpression = "ContentId in (";
var expressionAttributeValues = {};
for (var i = 0; i < currentFavorites.length; i++) {
var contentIdName = ":contentId"+(i+1);
if (i==0) {
filterExpression = filterExpression + contentIdName;
} else {
filterExpression = filterExpression + ", " + contentIdName;
}
expressionAttributeValues[contentIdName] = currentFavorites[i];
}
filterExpression = filterExpression + ")";
var params = {
TableName: environment.ddbContentTableName,
ProjectionExpression: "Title, ContentId, Link",
FilterExpression: filterExpression,
ExpressionAttributeValues: expressionAttributeValues
};
var docClient = new AWS.DynamoDB.DocumentClient();
docClient.scan(params, onQuery);
我也在寻找动态解决方案,而不是必须手动将每个参数名称放入条件表达式中。以下是一个解决方案:
List<String> valList= new ArrayList<String>(); // Populate the Values in a List
StringJoiner valMap = new StringJoiner(","); // This will be the dynamic Value Map
int i=1;
table = dynamoDB.getTable(myTable);
StringBuilder filterExpression = new StringBuilder();
Map<String, Object> eav = new HashMap<String, Object>();
if(!valList.isEmpty())
{
for(String attrVal: valList)
{
eav.put(":val"+i, attrVal);
valMap.add(":val"+i);
i++;
}
filterExpression.append("attrColName in ("+valMap.toString()+")"); //here attrColName is the DB attribute
}
ItemCollection<ScanOutcome> items;
items = table.scan(
filterExpression.toString(), //FilterExpression
null, //ProjectionExpression - choose all columns
null, //ExpressionAttributeNames - not used in this example
eav);//ExpressionAttributeValues
var params = {
TableName: "tableOne",
ProjectionExpression: "Title, ContentId, Link",
FilterExpression: "ContentId in (:contentIds)",
ExpressionAttributeValues: {":contentIds":[11,22,33,44,55]}
};
var docClient = new AWS.DynamoDB.DocumentClient();
docClient.scan(params);