Add missing Expression overloads for db.Exists<T>, impl currently uses Count > 0

Author: mythz

src/ServiceStack.OrmLite/OrmLiteReadConnectionExtensions.cs

@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.Data;
 using System.Linq;
+using System.Linq.Expressions;
 
 namespace ServiceStack.OrmLite
 {
@@ -291,6 +292,32 @@ public static Dictionary<K, V> DictionaryFmt<K, V>(this IDbConnection dbConn, st
             return dbConn.Exec(dbCmd => dbCmd.DictionaryFmt<K, V>(sqlFormat, sqlParams));
         }
 
+        /// <summary>
+        /// Returns true if the Query returns any records that match the LINQ expression, E.g:
+        /// <para>db.Exists&lt;Person&gt;(x =&gt; x.Age &lt; 50)</para>
+        /// </summary>
+        public static bool Exists<T>(this IDbConnection dbConn, Expression<Func<T, bool>> expression)
+        {
+            return dbConn.Exec(dbCmd => dbCmd.Count(expression)) > 0;
+        }
+
+        /// <summary>
+        /// Returns true if the Query returns any records that match the SqlExpression lambda, E.g:
+        /// <para>db.Exists&lt;Person&gt;(q =&gt; q.Where(x =&gt; x.Age &lt; 50))</para>
+        /// </summary>
+        public static bool Exists<T>(this IDbConnection dbConn, Func<SqlExpression<T>, SqlExpression<T>> expression)
+        {
+            return dbConn.Exec(dbCmd => dbCmd.Count(expression)) > 0;
+        }
+
+        /// <summary>
+        /// Returns true if the Query returns any records that match the supplied SqlExpression, E.g:
+        /// <para>db.Exists(db.SqlExpression&lt;Person&gt;().Where(x =&gt; x.Age &lt; 50))</para>
+        /// </summary>
+        public static bool Exists<T>(this IDbConnection dbConn, SqlExpression<T> expression)
+        {
+            return dbConn.Exec(dbCmd => dbCmd.Count(expression)) > 0;
+        }
         /// <summary>
         /// Returns true if the Query returns any records, using an SqlFormat query. E.g:
         /// <para>db.Exists&lt;Person&gt;(new { Age = 42 })</para>

tests/ServiceStack.OrmLite.Tests/ApiSqlServerTests.cs

@@ -163,6 +163,12 @@ public void API_SqlServer_Examples()
             db.DictionaryFmt<int, string>("SELECT Id, LastName FROM Person WHERE Age < {0}", 50);
             Assert.That(db.GetLastSql(), Is.EqualTo("SELECT Id, LastName FROM Person WHERE Age < 50"));
 
+            db.Exists<Person>(x => x.Age < 50);
+            Assert.That(db.GetLastSql(), Is.EqualTo("SELECT COUNT(*) FROM \"Person\" WHERE (\"Age\" < 50)"));
+
+            db.Exists(db.SqlExpression<Person>().Where(x => x.Age < 50));
+            Assert.That(db.GetLastSql(), Is.EqualTo("SELECT COUNT(*) FROM \"Person\" WHERE (\"Age\" < 50)"));
+
             db.Exists<Person>(new { Age = 42 });
             Assert.That(db.GetLastSql(), Is.EqualTo("SELECT \"Id\", \"FirstName\", \"LastName\", \"Age\" FROM \"Person\" WHERE \"Age\" = @Age"));
 

tests/ServiceStack.OrmLite.Tests/ApiSqliteTests.cs

@@ -164,6 +164,12 @@ public void API_Sqlite_Examples()
             db.DictionaryFmt<int, string>("SELECT Id, LastName FROM Person WHERE Age < {0}", 50);
             Assert.That(db.GetLastSql(), Is.EqualTo("SELECT Id, LastName FROM Person WHERE Age < 50"));
 
+            db.Exists<Person>(x => x.Age < 50);
+            Assert.That(db.GetLastSql(), Is.EqualTo("SELECT COUNT(*) FROM \"Person\" WHERE (\"Age\" < 50)"));
+
+            db.Exists(db.SqlExpression<Person>().Where(x => x.Age < 50));
+            Assert.That(db.GetLastSql(), Is.EqualTo("SELECT COUNT(*) FROM \"Person\" WHERE (\"Age\" < 50)"));
+
             db.Exists<Person>(new { Age = 42 });
             Assert.That(db.GetLastSql(), Is.EqualTo("SELECT \"Id\", \"FirstName\", \"LastName\", \"Age\" FROM \"Person\" WHERE \"Age\" = @Age"));