feat: create entities for invitations, attendees, and tags

backend/src/main/java/online/wesal/wesal/entity/Attendee.java

@@ -0,0 +1,67 @@
+package online.wesal.wesal.entity;
+
+import jakarta.persistence.*;
+import jakarta.validation.constraints.NotNull;
+import java.time.LocalDateTime;
+
+@Entity
+@Table(name = "attendees", 
+       uniqueConstraints = @UniqueConstraint(columnNames = {"invitation_id", "user_id"}))
+public class Attendee {
+    
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "invitation_id", nullable = false)
+    @NotNull
+    private Invitation invitation;
+    
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "user_id", nullable = false)
+    @NotNull
+    private User user;
+    
+    @Column(nullable = false)
+    private LocalDateTime joinedAt = LocalDateTime.now();
+    
+    public Attendee() {}
+    
+    public Attendee(Invitation invitation, User user) {
+        this.invitation = invitation;
+        this.user = user;
+    }
+    
+    public Long getId() {
+        return id;
+    }
+    
+    public void setId(Long id) {
+        this.id = id;
+    }
+    
+    public Invitation getInvitation() {
+        return invitation;
+    }
+    
+    public void setInvitation(Invitation invitation) {
+        this.invitation = invitation;
+    }
+    
+    public User getUser() {
+        return user;
+    }
+    
+    public void setUser(User user) {
+        this.user = user;
+    }
+    
+    public LocalDateTime getJoinedAt() {
+        return joinedAt;
+    }
+    
+    public void setJoinedAt(LocalDateTime joinedAt) {
+        this.joinedAt = joinedAt;
+    }
+}

backend/src/main/java/online/wesal/wesal/entity/Invitation.java

@@ -0,0 +1,138 @@
+package online.wesal.wesal.entity;
+
+import jakarta.persistence.*;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Positive;
+import java.time.LocalDateTime;
+
+@Entity
+@Table(name = "invitations")
+public class Invitation {
+    
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    
+    @Column(nullable = false)
+    @NotBlank
+    private String title;
+    
+    @Column(nullable = false, columnDefinition = "TEXT")
+    @NotBlank
+    private String description;
+    
+    private LocalDateTime dateTime;
+    
+    private String location;
+    
+    @Column(nullable = false)
+    @Positive
+    private Integer maxParticipants;
+    
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "tag_id", nullable = false)
+    @NotNull
+    private Tag tag;
+    
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "creator_id", nullable = false)
+    @NotNull
+    private User creator;
+    
+    @Column(nullable = false)
+    private Integer currentAttendees = 0;
+    
+    @Column(nullable = false)
+    private LocalDateTime createdAt = LocalDateTime.now();
+    
+    public Invitation() {}
+    
+    public Invitation(String title, String description, Integer maxParticipants, Tag tag, User creator) {
+        this.title = title;
+        this.description = description;
+        this.maxParticipants = maxParticipants;
+        this.tag = tag;
+        this.creator = creator;
+    }
+    
+    public Long getId() {
+        return id;
+    }
+    
+    public void setId(Long id) {
+        this.id = id;
+    }
+    
+    public String getTitle() {
+        return title;
+    }
+    
+    public void setTitle(String title) {
+        this.title = title;
+    }
+    
+    public String getDescription() {
+        return description;
+    }
+    
+    public void setDescription(String description) {
+        this.description = description;
+    }
+    
+    public LocalDateTime getDateTime() {
+        return dateTime;
+    }
+    
+    public void setDateTime(LocalDateTime dateTime) {
+        this.dateTime = dateTime;
+    }
+    
+    public String getLocation() {
+        return location;
+    }
+    
+    public void setLocation(String location) {
+        this.location = location;
+    }
+    
+    public Integer getMaxParticipants() {
+        return maxParticipants;
+    }
+    
+    public void setMaxParticipants(Integer maxParticipants) {
+        this.maxParticipants = maxParticipants;
+    }
+    
+    public Tag getTag() {
+        return tag;
+    }
+    
+    public void setTag(Tag tag) {
+        this.tag = tag;
+    }
+    
+    public User getCreator() {
+        return creator;
+    }
+    
+    public void setCreator(User creator) {
+        this.creator = creator;
+    }
+    
+    public LocalDateTime getCreatedAt() {
+        return createdAt;
+    }
+    
+    public void setCreatedAt(LocalDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+    
+    public Integer getCurrentAttendees() {
+        return currentAttendees;
+    }
+    
+    public void setCurrentAttendees(Integer currentAttendees) {
+        this.currentAttendees = currentAttendees;
+    }
+}

backend/src/main/java/online/wesal/wesal/entity/Tag.java

@@ -0,0 +1,65 @@
+package online.wesal.wesal.entity;
+
+import jakarta.persistence.*;
+import jakarta.validation.constraints.NotBlank;
+
+@Entity
+@Table(name = "tags")
+public class Tag {
+    
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    
+    @Column(nullable = false, unique = true)
+    @NotBlank
+    private String name;
+    
+    @Column(nullable = false)
+    @NotBlank
+    private String colorHex;
+    
+    @Column(nullable = false)
+    @NotBlank
+    private String iconName;
+    
+    public Tag() {}
+    
+    public Tag(String name, String colorHex, String iconName) {
+        this.name = name;
+        this.colorHex = colorHex;
+        this.iconName = iconName;
+    }
+    
+    public Long getId() {
+        return id;
+    }
+    
+    public void setId(Long id) {
+        this.id = id;
+    }
+    
+    public String getName() {
+        return name;
+    }
+    
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    public String getColorHex() {
+        return colorHex;
+    }
+    
+    public void setColorHex(String colorHex) {
+        this.colorHex = colorHex;
+    }
+    
+    public String getIconName() {
+        return iconName;
+    }
+    
+    public void setIconName(String iconName) {
+        this.iconName = iconName;
+    }
+}