Zlatko B.

90and10

Creating a content engine for businesses by leveraging AI.

Founder

Online Community

Whether you're a freelancer doing it on your own, running an agency, or thinking about shifting from freelancer to building your agency – it's not an easy journey. The path is filled with challenges, questions, and obstacles that can leave you feeling overwhelmed and unsure of your next steps.

This is where a community like this becomes vital to navigating the world of freelancing and agency craziness. Imagine having access to:

→ Resources to help you run your business more effectively.
→ Live chat with all community members, fostering collaboration and support.
→ Access to top freelancers and agency operators who have been in your shoes.
→ Events with guests from all walks of the agency and freelance world, sharing their insights and experiences.
→ Insights into marketing, sales, and making a real profit, so you can grow your business sustainably.

And much more, all designed to help you succeed on your freelance or agency journey.

Running a community

920Four

Helping businesses build brand awareness and authority through content across every platform.

Creative Consultant

What is My Brain?

Feed your entrepreneur energy on creative conversations with business owners behind the latest bright ideas on ‘What Is My Brain?’

Podcast Host

Tako Agency

Shop Circle

Helping shape the partnership program. Identifying growth strategies for all the different apps at Shop

Consulting and Strategy (Partnerships and Product Growth)

Over the past 10+ years, I went from being a freelance project manager to building a 7-figure agency that employs over 20 people.

I briefly stepped down as day-to-day CEO at Tako Agency in 2021 and started my product studio, 920Four.com. Now I run both agencies. 

I became interested in building SaaS products in early 2018 when I started Tako Agency, and my goal was to cater to the niche-SaaS business market. Since then, I have built Sparetoolz.com, Thymeline.co, and a few others, and more are in the works. 

I am a multi-passionate entrepreneur, and I am on a mission to help freelancers, early agency owners, and digital product builders grow their businesses. 

What I have done and what I am doing:

→ Currently building www.thymeline.co at www.920four.com.

→ Built Tako Agency | 7-figure eCommerce agency. 

→ Built Sparetoolz | a peer-to-peer tool rental marketplace. 

→ Built 920Four | Product studio focused on niche products.

→ Growing my personal brand | www.zlatkobijelic.com


Head over to my website → www.zlatkobijelic.com to find out more about me. 

Sign up for my newsletter → https://zlatkobijelic.com/newsletter

For eCommerce consulting → http://www.takoagency.com/contact-us

Practical .NET and Software Architecture Tips | Microsoft MVP

Hi there! 👋

I'm a senior software engineer, primarily working in the .NET ecosystem.

Things I talk about on LinkedIn:
- C# and .NET ❤
- Software engineering and architecture 
- Distributed systems and how to build them
- Databases and optimization techniques
- Career and personal growth

One of my goals (i̶s̶) was to become a Microsoft MVP in Developer Technologies.
I became an MVP in March of 2023.

If this sounds interesting, let's connect!

Milan Jovanović

I upgraded my Clean Architecture template to .NET 10.

And it took only a few minutes. Here's how 👇

My .NET version is defined in one place, a Build props file. I updated to net10 and that took care of all the projects in the solution.

The next part was updating the NuGet packages.

This was equally simple with central package management. I updated the version in the Packages props file, and it was picked up by all the projects in the solution.

Here's what's inside:
- Simple domain model with Domain Events pattern
- CQRS (no MediatR) + clean use cases implementation
- Validation and logging cross-cutting concerns
- Authentication with JWT and user context
- Boilerplate for RBAC authorization
- Docker Compose orchestration
- Minimal APIs, health checks

You can get the template here: https://lnkd.in/eihaFihr

I recently found out my template is used by a local company, doing $30M+ yearly revenue.

The .sln file as we know it is finally dead.

After nearly two decades of dealing with unreadable GUIDs and painful merge conflicts, Visual Studio 2026 has introduced the new .slnx format. It’s clean, it’s XML-based, and it actually makes sense.

But that’s not the only upgrade.

In my latest video, I show you how I moved my entire solution from .NET 9 to .NET 10 in just a few minutes.

The secret isn't upgrading every project manually, it’s using a "Smart Setup" with Directory.Build.props and Central Package Management.

In this video, I break down:

- How to change target frameworks for 20+ projects instantly
- Managing NuGet versions in one single file
- A deep dive into the new .slnx format (and how to migrate)
- Handling Dockerfile updates for .NET 10

Stop fighting with your solution files.

Here is the better way to handle the upgrade: https://lnkd.in/dFgdarZe

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Talks about #csharp, #dotnet, #databases, #softwareengineering, and #softwarearchitecture

I failed an interview because I didn't know how locks work in C#.

Read this to make sure it never happens to you.

I've told this story a couple of times before, but it's worth repeating.

I was in an interview some 7-8 years ago, doing a live coding exercise.

I was integrating with a currency conversion API and needed to add caching.

The problem was how this would scale with multiple concurrent requests.

A classic cache stampede problem.

I wanted to prevent this with locking.

Locking allows us to control how many threads can access some piece of code.

Note that I rarely worked with low-level code.

But the company I was interviewing for does.

Of course, they'd have this in the interview process.

Here's the situation:

- I knew I needed a locking mechanism
- But the method was async (oof!)
- So I tried to solve this using the `lock` statement

And that's where it all went to shit...

The `lock` statement doesn't work with async-await.

And it makes sense.

You can't guarantee which thread will complete the method.

So what's the solution?

You need to use an asynchronous synchronization primitive.

Luckily, C # has many to choose from.

Semaphore, SemaphoreSlim, Mutex, Monitor, etc.

Two important remarks:

1) Use a timeout when waiting on the semaphore
2) Always release the lock with a try-finally

Here's a tough question for you.

How would you implement a lock in a database?

If you want to find the answer, go here: https://lnkd.in/eVTMfu-y

Would you have nailed this interview?

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You can find security risks in your code at build time.

Here's a simple way you can implement this in .NET in a few minutes.

Imagine being able to find security risks when you build your code.

Static code analysis lets you do this.

Here's an example build error that warns me my password hashing code is insecure. 👇

Static code analysis can help you write secure and consistent code. And you can also enforce this at build, even in CI pipelines.

If you want to see how to set this up from scratch, check out this article: https://lnkd.in/dyYFpBYZ

Note that this doesn't detect every possible issue.

If you want to take this further, you can look at more powerful solutions like SonarQube.

---
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I love working with the Service Discovery library in .NET.

It's a lightweight configuration-based approach.

This actually came out of the effort done in Aspire.

If you're new to this concept, here's a quick breakdown.

Service discovery allows developers to reference external services using logical names instead of physical IP addresses and ports.

There's a centralized store for services to register themselves.

Clients can query the service registry to find the service's physical address.

The service discovery library for .NET is simpler, though.

It still lets you use logical names to refer to external services.

However, the discovery side is "lacking".

You have to specify the physical addresses in the application settings.

Here's a step-by-step tutorial: https://lnkd.in/eX4Wy3jD

You can configure the service URLs during deployment in your CI/CD pipelines.

Or even use a central configuration store (Azure App Configuration) for service discovery URLs.

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The riskiest line of code you'll write today is the one without a feature flag.

Fortunately, .NET has you covered right out of the box.

Feature flags are a software development technique that allows you to wrap application features in a conditional statement.

You can then toggle the feature on or off at runtime to control which features are enabled.

.NET already has feature flag support built in.

You can use the IFeatureManager in your code to check whether a feature is enabled.

Want to learn more about using feature flags?

Check out this article: https://lnkd.in/ddxmMg4V

There are many popular services for managing feature flags.

I've used LaunchDarkly often, and recently also PostHog (it offers many more features).

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If you're still writing five separate interfaces and classes for every single command in .NET, you need to see this.

For years, many of us in the .NET community have relied on MediatR and MassTransit for command handling and messaging. But the boilerplate is real.

I finally took the plunge and explored Wolverine, a library that claims to be the "next generation" of .NET messaging by focusing on convention over configuration.

In my new video, I share my raw, first-take as a long-time user of other messaging tools: https://lnkd.in/eDm9Aa3p

What's the fastest way to do a SQL bulk insert?

I tested out all the popular approaches...

SqlBulkCopy is your winner. It's the fastest way to insert a large amount of data into SQL Server. But it does require writing more code than the other approaches.

Postgres has the COPY command, which works similarly.

Here are 5 more solutions I compared: https://lnkd.in/eearSh_z

Which one would you use?

---
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The fastest way to do Bulk Inserts

Stop storing secrets in appsettings.json. Seriously.

That file was never meant to hold production credentials, yet I see it in real projects all the time.

I just published a new walkthrough where I show how to secure your .NET apps with Azure Key Vault:

- Creating your first Key Vault
- The exact RBAC roles you actually need
- Storing secrets with versioning
- Authenticating with DefaultAzureCredential
- Pulling secrets directly into ASPNET Core configuration
- Loading connection strings + options without touching appsettings

It’s a clean setup that keeps your sensitive values out of the repo and follows Azure’s best practices.

Learn more here: https://lnkd.in/eU4mUKnY

If you want to upgrade how you handle secrets in .NET, this one will help you get it right from the start.

Are you accidentally crippling your EF Core queries?

Before you start bashing on EF, this is an SQL problem, not an EF problem.

But it can be problematic to find and fix with EF.

Understand the Cartesian Explosion problem and how it occurs in your queries.

I'll give you a practical solution using EF Core's query-splitting feature.

Here's the full story: https://lnkd.in/ezv5B48v

In future versions of EF, the split queries will be batched, which should significantly improve performance. 

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EF Query splitting

I rewrote a 40-year-old APL system to a modern tech stack.

It powers a $10M manufacturing business with 460+ database tables.

Here are 5 lessons I learned in 4 years:

1. Start with core business logic first

2. Modular architecture is worth the investment

3. Data sync is harder than you think

4. Balance technical needs with business pressure

5. Document institutional knowledge before it's gone

Want the full story of our legacy migration journey?

Check out my blog post: https://lnkd.in/eacxqj7z

This project taught me so many things about enterprise architecture.

I think you'll learn a few things too.

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I like my API endpoints "thin".

If I can have controllers (or Minimal APIs) with 4-5 lines of code, that'd be best.

Here's why you should implement this.

The API endpoint's only responsibility becomes:

1. Accepting a request
2. Constructing a command/query object
3. Sending it to the respective handler and getting a result

The best part?

You don't need MediatR.

With it going commercial, I'm sure many people will switch away.

I implemented my custom solution with <100 lines of code.

Here's how: https://lnkd.in/dURSP2Bc

What do you think about this approach?

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Looking for a simple message bus in .NET?

I recommend taking a look at System Threading Channels.

You can implement a simple in-memory message bus using Channels in .NET.

Channels implement the producer-consumer pattern:

- Producers asynchronously produce data
- Consumers asynchronously consume that data

A channel has a Writer and Reader, that you can use to publish and consume messages. respectively.

Here's how you can use this to implement a simple message bus: https://lnkd.in/ekfJZd5n

Remember that this is still an in-memory bus, so it's not reliable.

You can implement resiliency around this, but it only goes so far.

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Clean code tip:

- Merge nested IF statements into one condition

I often make this simple change to improve code readability.

Clean code principles will make you a better developer.

But what is clean code in the first place?

Clean code is code that's:

- Easy to read
- Easy to maintain
- Easy to understand

Writing clean code is a skill.

It's a skill you can learn and improve with practice.

In the initial example:

- Nesting increases complexity
- Nesting makes the code harder to reason about

The solution is to combine the nested IF statements into a single IF.

Three ways you can do this:

- Write an inline boolean expression
- Expose a method with the expression
- Create a variable with the expression

But this is just the start.

Here are 8 more clean code tips: https://lnkd.in/dt84mr9J

Which solution do you like better?

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Implementing resilience in .NET? You better...

Polly is probably your first choice.

And Polly is much faster in V8+.

But why should you care about making your application resilient?

Let's say your services communicate by sending HTTP requests.

HTTP requests can fail because of network or server issues.

These failures can disrupt service availability, especially as dependencies increase. This increases the risk of cascading failures.

Luckily, there's a simple way to solve this in your .NET applications.

Here's how you can make your apps resilient: https://lnkd.in/e39__DXH

Do you use Polly in your applications?

There's also an official resilience library in .NET.

But it's a wrapper around Polly that adds OpenTelemetry on top.

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We all know the pain of code reviews.

You open a Pull Request (PR). You wait. And when you finally get feedback, it’s just nitpicks about formatting or style.

That doesn't help you ship better software. It just slows you down.

I’ve been testing out 𝗔𝘂𝗴𝗺𝗲𝗻𝘁 𝗖𝗼𝗱𝗲 and their new Code Review feature. I have to say, it feels different.

Most AI tools only look at the few lines of code you changed. They act like a basic spellchecker.

Augment acts like a Senior Engineer.

I typed auggie review on my PR, saw the little 👀 emoji pop up, and waited. Here is what surprised me:

1. 𝗜𝘁 𝗸𝗻𝗼𝘄𝘀 𝘁𝗵𝗲 𝘄𝗵𝗼𝗹𝗲 𝗽𝗶𝗰𝘁𝘂𝗿𝗲: It looks at your entire repository, not just the file you touched. It caught a breaking change I made that would have broken a different part of the app.

2. 𝗡𝗼 𝗻𝗼𝗶𝘀𝗲: It didn't nag me about style. It focused on real logic bugs and security risks.

3. 𝗜𝘁 𝗹𝗲𝗮𝗿𝗻𝘀 𝗺𝘆 𝗿𝘂𝗹𝗲𝘀: You can add a simple YAML file to teach it your team's specific guidelines.

It helps you catch the bad stuff, like edge cases and logic errors, before you merge.

If you want an AI that actually understands how you build software, give this a try.

Check it out here: https://fandf.co/4phaDOt

𝗠𝘆 𝗮𝗱𝘃𝗶𝗰𝗲: Don't skip the custom code review guidelines file. If you take five minutes to list your team's specific rules, the AI stops guessing and starts reviewing exactly the way you want it to. It saves you from repeating the same comments over and over.

Huge thanks to Augment Code for collaborating on this post with me.

Most modern APIs are stateless by default.

So how do you know who the current user is?

This is a common requirement: get the current user's information in a given request.

How can you do this in ASPNET Core?

You can create a class like the UserContext in the code snippet.

It uses the HttpContext to pull the user's information from the claims.

Here are a few more use cases for this: https://lnkd.in/dUKqKwCa

Would you use this in your applications?

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We’ve been faking left joins in LINQ for over a decade.

EF Core 10 finally adds native LeftJoin and RightJoin operators.

No more GroupJoin + DefaultIfEmpty just to express something every SQL dev understands instantly.

In this video, I break down:
- Why left joins in LINQ were always awkward
- What EF Core 10 actually ships (and what it doesn’t)
- Why this is about readability and intent, not performance
- Whether this change came too late (or right on time)

Same SQL. Much clearer code.

You can watch it here: https://lnkd.in/dtuYzayn

Was API Versioning a mistake?

I built and maintained a large public API (400+ endpoints).

The API has dozens of integrations, serving mainly mobile applications.

When your API is serving so many clients, breaking changes are expensive.

So, everything I implemented on the public API had to be planned.

If I wanted to introduce breaking changes, I had to version the API.

This wasn't a standard I decided on, but I had to live with the consequences.

API versioning allows your API to evolve independently from the clients using it - or so they say.

What we actually need is change management for APIs.

1. Don't remove anything
2. Don't change business rules
3. Don't make optional things required
4. New things must be optional

I explained this (and many other things) in-depth in Pragmatic REST APIs: https://lnkd.in/eXP53TP6

What do you think about API versioning?

P.S. I've got a Black Friday offer for my Pragmatic REST APIs course that expires soon. Don't miss it.

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Do you know all 3 service lifetimes in .NET?

ASPNET Core has three service lifetimes:
- Transient
- Singleton
- Scoped

Here's how they work. 👇

Transient services are created each time they're requested from the service container.

Scoped services are created once within the scope's lifetime. For ASP .NET Core applications, a new scope is created for each request. This is how you can resolve scoped services within a given request. You can also create a custom scope within a method, for example.

ASPNET Core applications also have a root service provider to resolve singleton services.

What if you want to resolve a scoped service inside a singleton service?

Here's what you will need to do: https://lnkd.in/eg_EQHb6

The solution isn't too complicated.

Save this for when you need it.

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The Battle

Zlatko B.

Milan Jovanović

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taplio

The Battle

Zlatko B.

Milan Jovanović

Followers

Posts

Engagements

Likes

Performance Score.css-goub6s{font-size:var(--chakra-fontSizes-md);font-weight:500;color:var(--chakra-colors-gray-600);display:block;margin-top:var(--chakra-space-1);}Milan Jovanović's LinkedIn Performance

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