Introduction to CouchDB with .NET part 14: list functions in design documents

June 14, 2017 Leave a comment

Introduction

In the previous post we looked at validation functions in CouchDB design documents. A validation function is used for data validation when inserting a new document or updating an existing one. It is called automatically upon an insert or update operation. We saw how to write a function that checks particular properties in the incoming document and throws an exception if it violates some business rules. We can also check whether the user executing the modification has a certain username or is in a user role, i.e. whether they are authorised to perform the action.

In this post we’ll look at lists in design documents.

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Continuation tasks in .NET TPL: a simple continuation example

June 13, 2017 Leave a comment

Tasks in .NET TPL make it easy to assign tasks that should run upon the completion of another task.

We’ll need a basic object with a single property:

public class Series
{
	public int CurrentValue
	{
		get;
		set;
	}
}

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Introduction to CouchDB with .NET part 13: validation functions in design documents

June 12, 2017 1 Comment

Introduction

In the previous post we saw some additional examples of MapReduce functions in CouchDB view design documents. First we investigated the built-in _sum reducer which – as its name applies – can be used to sum up numerical values of the keys from the map phase. The reducer can sum up integers, arrays of integers and objects whose properties are integers. Then we looked at how grouping works and then continued with a brief discussion of custom reducers. We can write our own reducers in JavaScript but we need to make sure that we always return a single value. If we need multiple values from a reducer then can wrap them in a JSON object and return that. Also, the usage of the rereduce parameter is confusing at first and we might only need it in large data sets.

In this post we’ll take a look at another type of functions in design documents, namely validation functions.

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Introduction to CouchDB with .NET part 12: more MapReduce examples

June 9, 2017 1 Comment

Introduction

In the previous post we first saw how to insert and update design documents via the HTTP API. It is not very different from the equivalent operations on “normal” data documents. However, we need to consider the keywords in a design documents such as “views”, “map” and “reduce”. We also saw how to select compound keys and values in the map function of the view index. Compound keys are very helpful when executing more complex queries such as “select all users above the age 20 and an address in Washington”. We went through a number of examples about limiting the range of the result set using the startkey and endkey query parameters.

In this post we’ll continue where we left off previously and go through more MapReduce examples.

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Parallel LINQ in .NET C#: a basic example

June 8, 2017 Leave a comment

Parallel LINQ – PLINQ – can be applied to LINQ to Objects. This type of LINQ which works with the IEnumerable and IEnumerable of T data types. There are extension methods in the PLINQ library that make parallel processing of the result from queries available. The result is that multiple data items are processed concurrently.

In fact it is not difficult to transform a “normal” LINQ statement to PLINQ.

Set up the data source:

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Introduction to CouchDB with .NET part 11: various MapReduce examples

June 7, 2017 1 Comment

Introduction

In the previous post we continued exploring view design documents in CouchDB. We first saw how to filter the documents that will be considered in the map phase. We then examined various simple operations on the key returned by the mapping. Our first reducer example included the usage of the built-in _count function for a simple count aggregation. Lastly we mentioned the usage of the stale query parameter to tell CouchDB how to handle the updating of the view indexes.

In this post we’ll continue looking at querying through views and MapReduce functions in CouchDB.

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Creating a detached child Task in .NET C#

June 6, 2017 Leave a comment

A child Task, a.k.a a nested Task, is a Task that’s started within the body of another Task. The containing Task is called the parent.

A detached child Task is one which doesn’t have any relationship with the parent. The detached child Task will be scheduled normally and will have no effect on the parent.

There’s nothing special about creating a detached child Task:

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Introduction to CouchDB with .NET part 10: view design documents cont’d

June 5, 2017 1 Comment

Introduction

In theprevious post we started looking into a large and relatively complex topic within CouchDB namely design documents. Design documents are JSON documents like the data documents we’ve looked at so far but they have a special purpose. They use JavaScript for their logic. The JS functions are embedded in the JSON document which has sections for each type of role a design document can play: view, update, show/list, validation. We started discussing the view design documents that play an important role in querying a CouchDB database. We also introduced the idea of MapReduce that is heavily used in view-based queries.

In this post we’ll continue where we left off in the previous part and continue looking at how view design documents work. We’ll keep using the children database we created previously.

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Introduction to CouchDB with .NET part 9: starting with view design documents

June 2, 2017 1 Comment

Introduction

In the previous post we looked at data replication in CouchDB. Data replication means that the documents of a source database are copied over to the target database. At the end of the replication process the source and target databases should have the exact same set of documents where even the revision IDs are the same. Data replication is a means of creating backups and archives. It is also great if we need to test a function on real-life production data. We can run the tests on the replicated data set as much as we want without any effect on the production system. Data replication can be a one-off event or a continuous flow of data synchronisation.

In this post we’ll start looking into a large topic within CouchDB, namely design documents.

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Examining a Type in .NET C#

June 1, 2017 Leave a comment

You can get hold of Types in a variety of ways. You can extract the Types available in an Assembly as follows:

Assembly executingAssembly = Assembly.GetExecutingAssembly();
Type[] typesAttachedToAssembly = executingAssembly.GetTypes();

Console.WriteLine("Types attached to executing assembly: ");
foreach (Type type in typesAttachedToAssembly)
{
	Console.WriteLine(type.FullName);
}

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