Key Value Operations

how-to

Documents

A document refers to an entry in the database (other databases may refer to the same concept as a row). A document has an ID (primary key in other databases), which is unique to the document and by which it can be located. The document also has a value which contains the actual application data. See the concept guide to Documents for a deeper dive into documents in the Couchbase Data Platform. Or read on, for a hands-on introduction to working with documents from the .NET SDK.

CRUD Operations

The core interface to Couchbase Server is simple KV operations on full documents. Make sure you’re familiar with the basics of authorization and connecting to a Cluster from the Start Using the SDK section. We’re going to expand on the short Upsert example we used there, adding options as we move through the various CRUD operations. Here is the Insert operation at its simplest:

Insert

var document = new {foo = "bar", bar = "foo"};
try {
    var result = await collection.InsertAsync("document-key", document);
}
catch (DocumentExistsException) {
    Console.WriteLine("Document already exists");
}

Options may be added to operations:

Insert (with options)

try {
    var document = new {foo = "bar", bar = "foo"};

    var result = await collection.InsertAsync("document-key", document,
        options =>
        {
            options.Expiry(TimeSpan.FromDays(1));
            options.Timeout(TimeSpan.FromSeconds(5));
        }
    );
}
catch (DocumentExistsException) {
    // handle exception
}

Setting a Compare and Swap (CAS) value is a form of optimistic locking - dealt with in depth in the CAS page. Here we just note that the CAS is a value representing the current state of an item; each time the item is modified, its CAS changes. The CAS value is returned as part of a document’s metadata whenever a document is accessed. Without explicitly setting it, a newly-created document would have a CAS value of 0.

Timeout is an optional parameter which in the .NET SDK has a type value of TimeSpan. Timeout sets the timeout value for the underlying network connection. We will add to these options for the Replace example:

var previousResult = await collection.GetAsync("document-key");
var cas = previousResult.Cas;

var document = new {foo = "bar", bar = "foo"};

var result = await collection.ReplaceAsync("document-key", document,
    options =>
    {
        options.Cas(cas);
        options.Expiry(TimeSpan.FromMinutes(1));
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

Expiration sets an explicit time to live (TTL) for a document. We’ll discuss modifying Expiration in more details below. For a discussion of item (Document) vs Bucket expiration, see the Expiration Overview page.

var document = new { foo = "bar", bar = "foo" };
var result = await collection.UpsertAsync("document-key", document,
    options =>
    {
        options.Expiry(TimeSpan.FromMinutes(1));
        options.Durability(PersistTo.One, ReplicateTo.One);
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

Here, we have add Durability options, namely PersistTo and ReplicateTo.

Durability

In Couchbase Server releases before 6.5, Durability was set with these two options — see the 6.0 Durability documentation — covering how many replicas the operation must be propagated to and how many persisted copies of the modified record must exist. If 6.5 or above is being used, you can take advantage of the Durable Write feature, in which Couchbase Server will only return success to the SDK after the requested replication level has been achieved. The three replication levels are:

Majority - The server will ensure that the change is available in memory on the majority of configured replicas.
MajorityAndPersistToActive - Majority level, plus persisted to disk on the active node.
PersistToMajority - Majority level, plus persisted to disk on the majority of configured replicas.

The options are in increasing levels of safety. Note that nothing comes for free - for a given node, waiting for writes to storage is considerably slower than waiting for it to be available in-memory. These trade offs, as well as which settings may be tuned, are discussed in the durability page.

The following example demonstrates using the newer durability features available in Couchbase server 6.5 onwards.

var document = new { foo = "bar", bar = "foo" };
var result = await collection.UpsertAsync("document-key", document,
    options =>
    {
        options.Expiry(TimeSpan.FromMinutes(1));
        options.Durability(DurabilityLevel.Majority);
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

If a version of Couchbase Server earlier than 6.5 is being used then the application can fall-back to 'client verified' durability. Here the SDK will do a simple poll of the replicas and only return once the requested durability level is achieved.

To stress, durability is a useful feature but should not be the default for most applications, as there is a performance consideration, and the default level of safety provided by Couchbase will be reasonable for the majority of situations.

Sub-Document Operations

All of these operations involve fetching the complete document from the Cluster. Where the number of operations or other circumstances make bandwidth a significant issue, the SDK can work on just a specific path of the document with Sub-Docunent Operations.

Retrieving full documents

Using the GetAsync() method with the document key can be done in a similar fashion to the other operations:

var previousResult = await collection.UpsertAsync("string-key", "string value");

var result = await collection.GetAsync("string-key");
var content = result.ContentAs<String>();

Timeout can also be set - as in the earlier Insert example:

Get (with options)

var result = await collection.GetAsync("string-key",
    options =>
    {
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);
var content = result.ContentAs<string>();

Removing

When removing a document, you will have the same concern for durability as with any additive modification to the Bucket:

Remove (with options)

var previousResult = await collection.GetAsync("document-key");

await collection.RemoveAsync("document-key",
    options =>
    {
        options.Cas(previousResult.Cas);
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

Expiration / TTL

By default, Couchbase documents do not expire, but transient or temporary data may be needed for user sessions, caches, or other temporary documents. Using Touch(), you can set expiration values on documents to handle transient data:

await collection.TouchAsync("document-key", TimeSpan.FromSeconds(10));

A network timeout can be set with the optional TouchOptions(), in the same fashion as earlier examples on this page:

await collection.TouchAsync("document-key", TimeSpan.FromSeconds(30),
    options =>
    {
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

If the absolute value of the expiry is less than 30 days (such as 60 * 60 * 24 * 30), it is considered an offset. If the value is greater, it is considered an absolute time stamp. For more on expiration see the expiration section of our documents discussion doc.

If you are using the overloads that take IDocument, note that the IDocument.Expiry property assumes ms (milli-seconds), and is converted to seconds before being sent to the server. All other overloads take a TimeSpan or an uint, and assume an expiry in seconds A time of zero will set the document to never expire (a negative number will set expiry to immediate — creating a tombstone). Values above 0ms but below 1000ms are rounded up to one second before being sent to the server — if you are using .NET SDK 3.0.4 or later.

Atomic Counters

The value of a document can be increased or decreased atomically using Binary.Increment() and Binary.Decrement().

Increment & Decrement are considered part of the ‘binary’ API and as such may still be subject to change

Increment

// increment binary value by 1, if document doesn’t exist, seed it at 1
await collection.Binary.IncrementAsync("binary-key");

Increment (with options)

await collection.Binary.IncrementAsync("binary-key",
options =>
    {
        options.Delta(1);
        options.Initial(1000);
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

Decrement

// decrement binary value by 1, if document doesn’t exist, seed it at 1
await collection.Binary.DecrementAsync("binary-key");

Decrement (with options)

await collection.Binary.DecrementAsync("binary-key",
    options =>
    {
        options.Delta(1);
        options.Initial(1000);
        options.Timeout(TimeSpan.FromSeconds(5));
    }
);

Setting the document expiry time only works when a document is created, and it is not possible to update the expiry time of an existing counter document with the Increment method — to do this during an increment, use with the Touch() method.

Atomicity Across Data Centers

If you are using Cross Data Center Replication (XDCR), be sure to avoid modifying the same counter in more than one datacenter. If the same counter is modified in multiple datacenters between replications, the counter will no longer be atomic, and its value can change in unspecified ways.

A counter must be incremented or decremented by only a single datacenter. Each datacenter must have its own set of counters that it uses — a possible implementation would be including a datacenter name in the counter document ID.

Scoped KV Operations

It is possible to perform scoped key value operations on named Collections with Couchbase Server release 7.0 onwards.

Here is an example showing an upsert in the users collection, which lives in the travel-sample.tenant_agent_00 keyspace:

var agentScope = await bucket.ScopeAsync("tenant_agent_00");
var usersCollection = await agentScope.CollectionAsync("users");

var content = new { name = "John Doe", preferred_email = "johndoe111@test123.test" };

var result = await usersCollection.UpsertAsync("user-key", content);

Additional Resources

Working on just a specific path within a JSON document will reduce network bandwidth requirements - see the Sub-Document pages.

Another way of increasing network performance is to pipeline operations with Batching Operations.

As well as various Formats of JSON, Couchbase can work directly with arbitary bytes, or binary format.

Our Query Engine enables retrieval of information using the SQL-like syntax of SQL++ (formerly N1QL).