增加模型验证IsIntAttribute，表示属性值ToString后必须可转换为Int

Falcon.SugarApi/ModelValidation/IsIntAttribute.cs

@@ -0,0 +1,28 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace Falcon.SugarApi.ModelValidation
+{
+    /// <summary>
+    /// 必须可转换为整数
+    /// </summary>
+    public class IsIntAttribute : ValidationAttribute
+    {
+        /// <inheritdoc />
+        public override bool IsValid(object? value) {
+            if (value == null) {
+                return false;
+            }
+            return int.TryParse(value.ToString(), out int _);
+        }
+
+        /// <inheritdoc />
+        protected override ValidationResult? IsValid(object? value, ValidationContext validationContext) {
+            if (value == null) {
+                return new ValidationResult(ErrorMessage = "必须为整数");
+            }
+            return this.IsValid(value) ? null
+                : new ValidationResult(ErrorMessage = "必须为整数", new List<string>() { validationContext.MemberName });
+        }
+    }
+}