BAEL-8258: Add examples for building SQL query strings

core-java-modules/core-java-collections-6/src/main/java/com/baeldung/querybuilder/SqlQueryBuilder.java

@@ -0,0 +1,103 @@
+package com.baeldung.querybuilder;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.SQLException;
+import java.util.StringJoiner;
+
+public class SqlQueryBuilder {
+
+    public String buildStudentQueryUsingWhereOneEqualsOne(
+            String enrollmentDate,
+            String birthDate) {
+
+        StringBuilder sb =
+                new StringBuilder(
+                        "SELECT id, name FROM Student WHERE 1=1");
+
+        if (enrollmentDate != null) {
+            sb.append(" AND enrollment_date = ?");
+        }
+
+        if (birthDate != null) {
+            sb.append(" AND birth_date = ?");
+        }
+
+        return sb.toString();
+    }
+
+
+    public String buildStudentQueryUsingStringConcatenation(
+        String enrollmentDate,
+        String birthDate) {
+
+    StringBuilder sb =
+            new StringBuilder(
+                    "SELECT id, name FROM Student");
+
+    if (enrollmentDate != null) {
+        sb.append(" WHERE enrollment_date = ?");
+    }
+
+    if (birthDate != null) {
+        sb.append(" AND birth_date = ?");
+    }
+
+    return sb.toString();
+}
+
+    public PreparedStatement createPreparedStatement(
+            Connection connection,
+            String enrollmentDate,
+            String birthDate) throws SQLException {
+
+        String sql = buildStudentQueryUsingWhereOneEqualsOne(
+                enrollmentDate,
+                birthDate);
+
+        PreparedStatement ps =
+                connection.prepareStatement(sql);
+
+        int parameterIndex = 1;
+
+        if (enrollmentDate != null) {
+            ps.setString(parameterIndex++, enrollmentDate);
+        }
+
+        if (birthDate != null) {
+            ps.setString(parameterIndex++, birthDate);
+        }
+
+        return ps;
+    }
+
+    public String buildQueryUsingStringJoiner(
+            boolean includeName,
+            boolean includeId,
+            boolean includeEnrollmentDate) {
+
+        String baseQuery = "SELECT * FROM Student";
+
+        StringJoiner whereClause =
+                new StringJoiner(" AND ");
+
+        if (includeName) {
+            whereClause.add("name LIKE ?");
+        }
+
+        if (includeId) {
+            whereClause.add("id = ?");
+        }
+
+        if (includeEnrollmentDate) {
+            whereClause.add("enrollment_date = ?");
+        }
+
+        if (whereClause.length() > 0) {
+            return baseQuery + " WHERE " + whereClause;
+        }
+
+        return baseQuery;
+    }
+
+}

core-java-modules/core-java-collections-6/src/test/java/com/baeldung/querybuilder/SqlQueryBuilderUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.querybuilder;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class SqlQueryBuilderUnitTest {
+
+    private final SqlQueryBuilder queryBuilder =
+            new SqlQueryBuilder();
+
+
+    @Test
+    void givenOnlyBirthDate_whenUsingStringConcatenation_thenGenerateInvalidSql() {
+
+        String query =
+                queryBuilder.buildStudentQueryUsingStringConcatenation(
+                    null,"2000-01-01");
+
+        assertEquals(
+                "SELECT id, name FROM Student AND birth_date = ?",
+                query);
+    }
+
+
+    @Test
+    void givenNoFilters_whenUsingWhereOneEqualsOne_thenReturnBaseQuery() {
+
+        String query =
+                queryBuilder.buildStudentQueryUsingWhereOneEqualsOne(
+                        null,
+                        null);
+
+        assertEquals(
+                "SELECT id, name FROM Student WHERE 1=1",
+                query);
+    }
+
+    @Test
+    void givenEnrollmentDate_whenUsingWhereOneEqualsOne_thenAppendCondition() {
+
+        String query =
+                queryBuilder.buildStudentQueryUsingWhereOneEqualsOne(
+                        "2024-01-01",
+                        null);
+
+        assertEquals(
+                "SELECT id, name FROM Student WHERE 1=1 AND enrollment_date = ?",
+                query);
+    }
+
+    @Test
+    void givenAllFilters_whenUsingWhereOneEqualsOne_thenAppendAllConditions() {
+
+        String query =
+                queryBuilder.buildStudentQueryUsingWhereOneEqualsOne(
+                        "2024-01-01",
+                        "2000-01-01");
+
+        assertEquals(
+                "SELECT id, name FROM Student WHERE 1=1 AND enrollment_date = ? AND birth_date = ?",
+                query);
+    }
+
+    @Test
+    void givenSelectedFilters_whenUsingStringJoiner_thenBuildWhereClause() {
+
+        String query =
+                queryBuilder.buildQueryUsingStringJoiner(
+                        true,
+                        false,
+                        true);
+
+        assertEquals(
+                "SELECT * FROM Student WHERE name LIKE ? AND enrollment_date = ?",
+                query);
+    }
+
+    @Test
+    void givenNoFilters_whenUsingStringJoiner_thenReturnBaseQuery() {
+
+        String query =
+                queryBuilder.buildQueryUsingStringJoiner(
+                        false,
+                        false,
+                        false);
+
+        assertEquals(
+                "SELECT * FROM Student",
+                query);
+    }
+
+}