Web Development
Making your code neater with TypeScript Paths

Making your code neater with TypeScript Paths

When I started doing development with TypeScript one of the first things that irked me was all those relative paths in import statements.

Code organisation and creating layers for maintainability is one of the things I'm most OCD about, so things like a service to call Prismics API end up in a folder called services. However, to then use it in a NextJs page a few folders deep ends up with an import statement such as this.

1import { prismicService } from '../../../src/services/Prismic/Prismic.service'

Yuck. Look at all those ../../ and to make things worse this also means if you move a file its no longer pointing in the right place.

Fortunately, there is a solution. Typescript supports path mapping through the tsconfig.json file.

First set a base URL property in the compiler options. 

1{
2  "compilerOptions": {
3    "baseUrl": ".", 
4  }
5}

At this point, you could get rid of all those ../ and just start at the src. e.g.

1import { prismicService } from 'src/services/Prismic/Prismic.service'

This is a lot better and we can now move files around, but it's still not perfect. The fact it's in a folder called src is a bit irrelevant for my liking.

Using the path's property we can define a grouping even lower down. e.g.

1// tsconfig.json
2{
3  "compilerOptions": {
4    "baseUrl": ".", 
5    "paths": {
6      "@Services/*": ["src/services/*"]
7    }
8  }
9}
10

11// New import
12import { prismicService } from '@Services/Prismic/Prismic.service'

For more information on TypeScript paths check out the official documentation here.

Going a bit further

As well as just making your code a bit easier to read. This also makes a simple solution to swapping out code in a way that would otherwise need a dependency injection framework.

Coming from a .net background where dependency injection and interfaces are frequently used there can be a desire to do it with TypeScript too. Although it is possible (you can read my blog post on dependency injection with NextJs and Tsyringe here) it has quite a heavy overhead to the amount of code you need to write.

A simpler solution can be like what Vercel have done in NextJs commerce for the different providers.

Check out this part of their tsconfig file.

1    "paths": {
2      "@lib/*": ["lib/*"],
3      "@utils/*": ["utils/*"],
4      "@config/*": ["config/*"],
5      "@assets/*": ["assets/*"],
6      "@components/*": ["components/*"],
7      "@commerce": ["../packages/commerce/src"],
8      "@commerce/*": ["../packages/commerce/src/*"],
9      "@framework": ["../packages/local/src"],
10      "@framework/*": ["../packages/local/src/*"]
11    }

That @framework section at the end defaults to local, but gets swapped out to a commerce provider like bigcommerce or shopify. As each one implements the same methods, anything importing from @framework simply uses the correct code when the solution is built.

Combining GROUP BY and CASE in a Linq Query

Combining GROUP BY and CASE in a Linq Query

With SQL Server you have the ability to make changes to the raw table field data within a GROUP BY clause by using a CASE statement. e.g.

1SELECT [QuestionId]
2      ,CASE WHEN Answer LIKE 'Other%' THEN 'Other'
3			ELSE Answer END AS [Answer]
4      ,count(*) as Count
5  FROM [SurveyResults-Q4-2022]
6  GROUP BY	QuestionId, 
7		CASE WHEN Answer LIKE 'Other%' THEN 'Other'
8		     ELSE Answer END

When using EF Core though rather than writing SQL directly we write Linq queries which get translated to the appropriate SQL query.

To achieve a CASE statement in a GROUP BY you can write the following.

1var q = from r in _context.SurveyResultsQ42022s
2        group r by new { r.QuestionId, Answer = (r.Answer.StartsWith("Other") ? "Other" : r.Answer) }
3        into g
4        select new { g.Key.QuestionId, g.Key.Answer, Count = g.Count() };
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Turning flat data into a hierarchy using C#

Turning flat data into a hierarchy using C#

Sometimes you have flat data and what you really want is a hierarchy. This can often happen when data is stored in a relational database that you want to return as JSON in an API. One SQL call will return a flat structure, but as JSON can give a complete hierarchy it makes more sense to convert it.

Let's assume we have the following as our source data:

1{
2  Country: "UK",
3  City: "London",
4  Population: 8800000
5}, {
6  Country: "UK",
7  City: "Edinburgh",
8  Population: 495400
9}, {
10  Country: "France",
11  City: "Paris",
12  Population: 2244000
13}

What we want to create is a structure like this:

1{
2  Country: "UK",
3  Cities: [
4    {
5      City: "London",
6      Population: 8800000
7    }, {
8      City: "Edinburgh",
9      Population: 495400
10    }]  
11}, {
12  Country: "France",
13  Cities: [
14    {
15      City: "Paris",
16      Population: 2244000
17   }]
18}

To make the conversion of flat data to a hierarchy using C# we can use a LInq expression.

First I need two models to represent the final structure. One to represent the Country and the other to represent the City. The Country class contains a list of cities.

1public class Country {
2    public string Country { get; set; }
3    public List<City> Cities{ get; set; }
4}
5

6public class City {
7    public string City { get; set; }
8    public int Population { get; set; }
9}

The following Linq query will then create a list of Countries populating the City list by doing a sub-select on the original dataset.

1// flatData contains our flat data
2var groupedByCountry = flatData.ToList()
3   .GroupBy(x => new { x.Country })
4   .Select(y => new Country() { 
5       Country = y.Key.Country, 
6       Cities = y.Select(c => new City() { 
7            City = c.City, 
8            Population = c.Population }).ToList() 
9   });