Specification pattern for dynamic queries in Spring Boot - Step-by-Step Execution

Concept Flow - Specification pattern for dynamic queries

Start: Receive filter criteria

↓

Create Specification objects

↓

Combine Specifications with AND/OR

↓

Pass Specification to Repository

↓

Repository builds query dynamically

↓

Execute query and return results

↓

End

The flow starts with filter criteria, builds Specification objects, combines them, passes to repository which creates and runs the query dynamically.

Execution Sample

Spring Boot

Specification<Person> spec = where(nameContains("John"))
  .and(ageGreaterThan(25));
List<Person> results = personRepository.findAll(spec);

This code creates a Specification to find people named John older than 25, then fetches matching results.

Execution Table

Step	Action	Specification State	Query Part	Result
1	Call nameContains("John")	Spec: name like '%John%'	WHERE name LIKE '%John%'	Spec created
2	Call ageGreaterThan(25)	Spec: age > 25	AND age > 25	Spec created
3	Combine with AND	Spec: name like '%John%' AND age > 25	WHERE name LIKE '%John%' AND age > 25	Combined Spec
4	Pass Spec to repository	Spec ready	Query built dynamically	Query ready
5	Execute query	Spec unchanged	Query runs	List<Person> returned
6	End	Spec unchanged	Query complete	Results delivered

💡 Query executes after combining all Specifications and returns matching results.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
spec	null	nameContains("John") Spec	ageGreaterThan(25) Spec separate	Combined Spec with AND	Passed to repo	Used in query	Unchanged

Key Moments - 3 Insights

How do multiple Specifications combine to form one query?

They combine using logical operators like AND or OR, as shown in step 3 of the execution_table where two specs merge into one combined spec.

Does the Specification execute the query by itself?

No, the Specification only builds the query conditions. The repository executes the query as shown in step 5.

Can Specifications be reused or combined dynamically?

Yes, Specifications are modular and can be combined dynamically before passing to the repository, demonstrated in steps 1-3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the Specification state after step 3?

A Spec: name like '%John%' OR age > 25

B Spec: age > 25 only

C Spec: name like '%John%' AND age > 25

D Spec: name like '%John%' only

💡 Hint

Check the 'Specification State' column at step 3 in the execution_table.

At which step does the repository build the query dynamically?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Query Part' column to find when 'Query built dynamically' happens.

If we add another Specification with OR instead of AND, how would the combined Specification state change at step 3?

A Spec: name like '%John%' AND age > 25

B Spec: name like '%John%' OR age > 25

C Spec: name like '%John%' only

D Spec: age > 25 only

💡 Hint

Think about how logical operators combine Specifications as shown in step 3.

Concept Snapshot

Specification pattern builds reusable query conditions.
Combine Specifications with AND/OR to form complex queries.
Pass combined Specification to Spring Data repository.
Repository dynamically builds and runs the query.
Allows flexible, dynamic filtering without hardcoding queries.

Full Transcript

The Specification pattern in Spring Boot helps build dynamic database queries by creating small reusable conditions called Specifications. Each Specification represents a filter, like 'name contains John' or 'age greater than 25'. These Specifications can be combined using logical operators like AND or OR to form complex queries. The combined Specification is then passed to the repository, which builds the actual database query dynamically and executes it. This approach avoids hardcoding queries and allows flexible filtering based on user input or other criteria. The execution flow starts with creating Specifications, combining them, passing to the repository, and finally executing the query to get results.