Introduction to CouchDB with .NET part 18: Mango indexes and queries continued

June 23, 2017 1 Comment

Introduction

In the previous post we started discussing a new feature in CouchDB 2.0, namely Mango queries. Mango queries and Mango indexes are also based on views but these views are created for us, we don’t need to worry about them. Therefore Mango queries provide us with a tool to perform ad-hoc searches in CouchDB with a JSON-based query language. We spent most of the previous post on setting up a small database of ZIP codes that we use for our demos. The gateway to performing the queries is the POST /_find endpoint in the HTTP API. We attach the query to the HTTP request body. We looked at the various properties of the query where the selector is the most important. We also saw that the _id property is indexed by default and then carried out our first query based on the id.

In this post we’ll continue looking at Mango queries.

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Combinable enumerations in C# .NET

June 22, 2017 1 Comment

You’ve probably encountered cases with combined enum values using the pipe character, i.e. the “bitwise or” operator ‘|’:

Size.Large | Size.ExtraLarge

Let’s see an example of how to create such an enum.

The enumeration is decorated with the Flags attribute like in the following example:

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Introduction to CouchDB with .NET part 17: starting with Mango queries

June 21, 2017 1 Comment

Introduction

In the previous post we discussed update design documents in CouchDB. Update functions make updating a document easier. They are not executed automatically when a document is updated. Instead, they must be called actively through a HTTP call. Update functions can make the update process easier since we don’t need to supply the revision ID. Also, they can have their own logic and add new rows to the document. An additional benefit is that we can send in the fields to be updated through the JSON body of the HTTP request. In other words we don’t need to provide all the properties of the document like in the case of a normal update we saw earlier.

In this post we’ll start looking into a brand new feature of CouchDB 2.0: Mango queries. A large part of the post is dedicated to setting up a ZIP code database that is slightly bigger than the demo databases we’ve been working with so far.

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How to pass any number of parameters into a method in C# .NET

June 20, 2017 Leave a comment

You must have come across built-in methods in .NET where you can send any number of arguments into a method. E.g. string.Format has an overload where you can pass in a format string and then an array with the “params” modifier.

There’s nothing stopping you from using the same keyword to write a similar method, here’s an example:

public void MethodWithParams(int toBeMultiplied, params int[] multipliers)
{
	foreach (int m in multipliers)
	{ 
		Console.WriteLine(string.Format("{0} x {1} = {2}", toBeMultiplied, m, toBeMultiplied * m));
	}
}

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Introduction to CouchDB with .NET part 16: update functions in design documents

June 19, 2017 3 Comments

Introduction

In the previous post we saw how show functions work in design documents. Show functions are applied on a single document and are able to transform that document into a different format. The formats can range from simple string manipulations to HTML reports. The show function has access to the HTTP request as well with its rich object which contains the request headers, the cookies, the query parameters and much more. Therefore the HTTP request can also be used to refine the logic within a show function.

In this post we’ll look at the last remaining design document function type called update functions.

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Various return types through choices in F#

June 18, 2017 Leave a comment

F# has a type called Choice which makes it possible for a function to return values of different types. A function can return either a boolean, or a string or an integer wrapped in a Choice object. So in fact the function still returns a single return type, i.e. a Choice, but the type contained within a Choices can vary.

Choices are represented by specialised ChoiceOf objects such as Choice1Of2 or Choice2Of7. If a function has, say, 3 possible return types then it must be able return 3 objects: Choice1Of3, Choice2Of3 and Choice3Of3. Let’s see an example:

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Options in F#

June 17, 2017 1 Comment

There are functions whose purpose is to locate an object in a collection or database. They either find the resource or they don’t. In case they find it then they return it from the function body. What if the resource is not found? E.g. we might be looking for the first number above 100 in an integer list. Then it is either found or not, we don’t know in advance. Mainstream OOP languages like C# or Java would return null or the maybe the default value of the type that’s being searched.

In F# we have the Option object to solve this problem. F# understands the “null” keyword as well but it’s mainly used when interacting with other .NET languages. Otherwise F# has no real notion of null as in an object that’s not pointing to an address in memory. F#’s approximation of a missing value is an Option that has no enclosed object. It’s called None. None is an object that indicates missing data which is not the same as null. Its opposite is called Some which has an enclosed object of some type. Both Some and None create an instance of type Option but None contains nothing.

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Introduction to CouchDB with .NET part 15: show functions in design documents

June 16, 2017 1 Comment

Introduction

In the previous post we took a look at lists in CouchDB design documents. Lists operate in conjunction with views. A list function has access to the output of a view and can transform it into a different data set. Lists do not change the underlying data at all, they are a type of extension to views. A list can output simple JSON or advanced HTML for fancy reports. We have access to the HTTP request object within the list function. The output of a list function can thus depend on stuff like query parameters, request headers, cookies etc.

In this post we’ll look at another function type in design documents called show functions.

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How to hide the key pressed in a .NET console application

June 15, 2017 Leave a comment

You probably know how to read the key pressed by the user in a .NET console application by the Console.ReadKey() method:

ConsoleKeyInfo pressedKey = Console.ReadKey();
Console.WriteLine("You have pressed: {0}", pressedKey.Key);

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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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