Lecture 9, 10 and 11 : Command Handlers

Initial_Projects/NoBS/src/main/java/com/example/demo/Command.java

@@ -0,0 +1,12 @@
+package com.example.demo;
+
+import org.springframework.http.ResponseEntity;
+
+
+public interface Command <E, T> {
+    // <E, T> = Entity, T is generic type in java
+
+    ResponseEntity <T> execute(E entity);
+    // we can also name the method handle.. since its a handler.. but execute is also used..
+
+}

Initial_Projects/NoBS/src/main/java/com/example/demo/Product/Model/UpdateProductCommand.java

@@ -0,0 +1,14 @@
+package com.example.demo.Product.Model;
+
+import lombok.Data;
+
+@Data
+public class UpdateProductCommand {
+    private int id;
+    private Product product;
+
+    public UpdateProductCommand(int id, Product product) {
+        this.id = id;
+        this.product = product;
+    }
+}

Initial_Projects/NoBS/src/main/java/com/example/demo/Product/ProductController.java

@@ -1,6 +1,10 @@
 package com.example.demo.Product;
 
 import com.example.demo.Product.Model.Product;
+import com.example.demo.Product.Model.UpdateProductCommand;
+import com.example.demo.Product.commandHandlers.CreateProductCommandHandler;
+import com.example.demo.Product.commandHandlers.DeleteProductCommandHandler;
+import com.example.demo.Product.commandHandlers.UpdateProductCommandHandler;
 import com.example.demo.Product.queryHandlers.GetAllProductsQueryHandler;
 import com.example.demo.Product.queryHandlers.GetProductQueryHandler;
 import org.apache.coyote.Response;
@@ -75,39 +79,67 @@ public ResponseEntity<Product> getProduct(@PathVariable Integer id) {
         return getProductQueryHandler.execute(id);
     }
 
-    // Lecture - 5: POST, PUT and DELETE MAPPING
+//    // Lecture - 5: POST, PUT and DELETE MAPPING
+//    @PostMapping
+//    // @RequestBody will tell that in the HTTP request body look for a product.
+//    public ResponseEntity createProduct(@RequestBody Product product) {
+//        // Accept a product through JSON
+//        // Convert it to a Product
+//        // Save it in the database
+//        productRepository.save(product); // Currently we do not have any data validation.
+//        return ResponseEntity.ok().build(); // This wont return anything in the body for now. Only returns a 200
+//                                            // response code.
+//    }
+
+    // Lecture 9 : Command Handler
+    @Autowired
+    private CreateProductCommandHandler createProductCommandHandler;
     @PostMapping
     // @RequestBody will tell that in the HTTP request body look for a product.
-    public ResponseEntity createProduct(@RequestBody Product product) {
-        // Accept a product through JSON
-        // Convert it to a Product
-        // Save it in the database
-        productRepository.save(product); // Currently we do not have any data validation.
-        return ResponseEntity.ok().build(); // This wont return anything in the body for now. Only returns a 200
-                                            // response code.
+    public ResponseEntity<String> createProduct(@RequestBody Product product) {
+        return createProductCommandHandler.execute(product);
     }
 
     // PUT is kind of a combination of GET AND POST.
+//    @PutMapping("/{id}")
+//    public ResponseEntity updateProduct(@PathVariable Integer id, @RequestBody Product product) {
+//        // We would require the id to update the product
+//        // Again we are not doing any validation here.
+//        // We are doing this id thing manually just to see. We could have passed the ID
+//        // in the product itself.
+//        product.setId(id); // Helps set the id so that retrieval / update becomes easy.
+//        productRepository.save(product); // updates the given product for the id set above.
+//        return ResponseEntity.ok().build();
+//    }
+
+    // Lecture 10 : Command Handler 2
+    @Autowired
+    UpdateProductCommandHandler updateProductCommandHandler;
     @PutMapping("/{id}")
     public ResponseEntity updateProduct(@PathVariable Integer id, @RequestBody Product product) {
-        // We would require the id to update the product
-        // Again we are not doing any validation here.
-        // We are doing this id thing manually just to see. We could have passed the ID
-        // in the product itself.
-        product.setId(id); // Helps set the id so that retrieval / update becomes easy.
-        productRepository.save(product); // updates the given product for the id set above.
-        return ResponseEntity.ok().build();
+        UpdateProductCommand updateProductCommand = new UpdateProductCommand(id, product);
+        return updateProductCommandHandler.execute(updateProductCommand);
     }
 
+//    @DeleteMapping("/{id}")
+//    public ResponseEntity deleteProduct(@PathVariable Integer id) {
+//        Product product = productRepository.findById(id).get();
+//        productRepository.delete(product);
+//
+//        // OR..
+//        // productRepository.deleteById(id);
+//
+//        return ResponseEntity.ok().build();
+//    }
+
+    // Lecture 11 : Command Handler 3
+    @Autowired
+    private DeleteProductCommandHandler deleteProductCommandHandler;
     @DeleteMapping("/{id}")
     public ResponseEntity deleteProduct(@PathVariable Integer id) {
-        Product product = productRepository.findById(id).get();
-        productRepository.delete(product);
-
-        // OR..
-        // productRepository.deleteById(id);
-
-        return ResponseEntity.ok().build();
+        // Not fully done yet as we have not handled the Optional (nullable) yet... in case we don't find the product with the given id.
+        // It'd be done in further classes with custom exception...
+        return deleteProductCommandHandler.execute(id);
     }
 
 }

Initial_Projects/NoBS/src/main/java/com/example/demo/Product/commandHandlers/CreateProductCommandHandler.java

@@ -0,0 +1,47 @@
+package com.example.demo.Product.commandHandlers;
+
+import com.example.demo.Command;
+import com.example.demo.Product.Model.Product;
+import com.example.demo.Product.ProductRepository;
+import io.micrometer.common.util.StringUtils;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+
+// Lecture 9 : Command Handler
+@Service
+public class CreateProductCommandHandler implements Command<Product, String> {
+
+    @Autowired // allows us to inject the product repository and access it in the command handler.
+    private ProductRepository productRepository;
+    @Override
+    public ResponseEntity<String> execute(Product product) {
+        // Validate then save...
+        checkValidation(product);
+
+        // Validation provides the safety for our app here...
+        // The validation won't allow to save a wrong product and will throw an exception and stop execution.
+
+        productRepository.save(product);
+        return ResponseEntity.ok().build();
+    }
+
+    private void checkValidation(Product product) {
+        // name
+        if (StringUtils.isBlank(product.getName())) { // micrometer utils... check import
+            throw new RuntimeException("Product name cannot be empty");
+        }
+        // description
+        if(StringUtils.isBlank(product.getDescription())) {
+            throw new RuntimeException("Description cannot be empty");
+        }
+        // price
+        if(product.getPrice() <= 0.0) {
+            throw new RuntimeException("Price cannot be negative or 0");
+        }
+        // quantity
+        if(product.getQuantity() <= 0) {
+            throw new RuntimeException("Quantity cannot be negative or 0");
+        }
+    }
+}

Initial_Projects/NoBS/src/main/java/com/example/demo/Product/commandHandlers/DeleteProductCommandHandler.java

@@ -0,0 +1,21 @@
+package com.example.demo.Product.commandHandlers;
+
+import com.example.demo.Command;
+import com.example.demo.Product.Model.Product;
+import com.example.demo.Product.ProductRepository;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+
+@Service
+public class DeleteProductCommandHandler implements Command<Integer, ResponseEntity> {
+
+    @Autowired
+    private ProductRepository productRepository;
+    @Override
+    public ResponseEntity<ResponseEntity> execute(Integer id) {
+        Product product = productRepository.getReferenceById(id);
+        productRepository.delete(product);
+        return ResponseEntity.ok().build();
+    }
+}

Initial_Projects/NoBS/src/main/java/com/example/demo/Product/commandHandlers/UpdateProductCommandHandler.java

@@ -0,0 +1,49 @@
+package com.example.demo.Product.commandHandlers;
+
+import com.example.demo.Command;
+import com.example.demo.Product.Model.Product;
+import com.example.demo.Product.Model.UpdateProductCommand;
+import com.example.demo.Product.ProductRepository;
+import io.micrometer.common.util.StringUtils;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+
+@Service
+public class UpdateProductCommandHandler implements Command<UpdateProductCommand, ResponseEntity> {
+
+    @Autowired
+    private ProductRepository productRepository;
+    @Override
+    public ResponseEntity execute(UpdateProductCommand command) {
+        Product product = command.getProduct();
+        // validate product
+        checkValidation(product);
+        product.setId(command.getId());
+        // If this is not done and the entry does not already exist in the database
+        // then it will work just like POST command else it will create a new entry.
+        productRepository.save(product);
+        return ResponseEntity.ok().build();
+    }
+
+    // This method could be abstracted even more as it is being used in multiple classes...
+    // by making something like another utility class
+    private void checkValidation(Product product) {
+        // name
+        if (StringUtils.isBlank(product.getName())) { // micrometer utils... check import
+            throw new RuntimeException("Product name cannot be empty");
+        }
+        // description
+        if(StringUtils.isBlank(product.getDescription())) {
+            throw new RuntimeException("Description cannot be empty");
+        }
+        // price
+        if(product.getPrice() <= 0.0) {
+            throw new RuntimeException("Price cannot be negative or 0");
+        }
+        // quantity
+        if(product.getQuantity() <= 0) {
+            throw new RuntimeException("Quantity cannot be negative or 0");
+        }
+    }
+}

Initial_Projects/db/NoBS.sql

@@ -2,13 +2,15 @@
 
 use nobs;
 
+/*
 CREATE TABLE product (
 	id INT AUTO_INCREMENT PRIMARY KEY,
     name VARCHAR(255),
     description VARCHAR(255),
     price double,
     quantity int
 );
+*/
 
 select * from product;