diff --git a/docs/installation.md b/docs/installation.md
index 9c2d9a5..aad5ed6 100644
--- a/docs/installation.md
+++ b/docs/installation.md
@@ -3,6 +3,20 @@
 ## Gradle
 ```kotlin
 // build.gradle.kts
+
+buildscript {
+    repositories {
+        maven { url = uri("https://jitpack.io") }
+    }
+    dependencies {
+        classpath("com.github.flecomte:postgres-json:+")
+    }
+}
+
+repositories {
+    maven { url = uri("https://jitpack.io") }
+}
+
 dependencies {
     implementation("com.github.flecomte:postgres-json:+")
 }
diff --git a/src/main/kotlin/fr/postgresjson/connexion/Function.kt b/src/main/kotlin/fr/postgresjson/connexion/Function.kt
index 83096f6..482747b 100644
--- a/src/main/kotlin/fr/postgresjson/connexion/Function.kt
+++ b/src/main/kotlin/fr/postgresjson/connexion/Function.kt
@@ -97,7 +97,7 @@ class Function(val definition: Function, override val connection: Connection) :
     }
 
     private fun compileArgs(values: Map<String, Any?>): String {
-        val parameters = definition.getParametersIndexedByName()
+        val parameters = definition.parametersIndexedByName
         val placeholders = values
             .filter { entry ->
                 val parameter = parameters[entry.key] ?: parameters["_" + entry.key] ?: error("Parameter ${entry.key} of function ${definition.name} not exist")
diff --git a/src/main/kotlin/fr/postgresjson/connexion/Requester.kt b/src/main/kotlin/fr/postgresjson/connexion/Requester.kt
index 75626a4..85c771b 100644
--- a/src/main/kotlin/fr/postgresjson/connexion/Requester.kt
+++ b/src/main/kotlin/fr/postgresjson/connexion/Requester.kt
@@ -63,6 +63,10 @@ class Requester(
 
     fun getQuery(path: String): Query = queries[path] ?: throw NoQueryDefined(path)
 
+    fun <A> inTransaction(block: Requester.() -> A?): A? = connection.inTransaction {
+        this@Requester.block()
+    }
+
     class NoFunctionDefined(name: String) : Exception("No function defined for $name")
     class NoQueryDefined(path: String) : Exception("No query defined in $path")
 }
diff --git a/src/main/kotlin/fr/postgresjson/definition/Function.kt b/src/main/kotlin/fr/postgresjson/definition/Function.kt
index 1afa240..707a6eb 100644
--- a/src/main/kotlin/fr/postgresjson/definition/Function.kt
+++ b/src/main/kotlin/fr/postgresjson/definition/Function.kt
@@ -1,5 +1,7 @@
 package fr.postgresjson.definition
 
+import fr.postgresjson.utils.Algorithm.MD5
+import fr.postgresjson.utils.hash
 import java.nio.file.Path
 
 class Function(
@@ -48,19 +50,26 @@ class Function(
 
     class FunctionNotFound(cause: Throwable? = null) : Resource.ParseException("Function not found in script", cause)
 
-    fun getDefinition(): String {
-        return parameters
-            .filter { it.direction == Parameter.Direction.IN }
-            .joinToString(", ") { "${it.name} ${it.type}" }
-            .let { "$name ($it)" }
-    }
+    val definition: String
+        get() {
+            return parameters
+                .filter { it.direction == Parameter.Direction.IN }
+                .joinToString(", ") { "${it.name} ${it.type}" }
+                .let { "$name ($it)" }
+        }
 
-    fun getParametersIndexedByName(): Map<String, Parameter> {
-        return parameters.associateBy { it.name }
-    }
+    val definitionHash: String
+        get() {
+            return definition.hash(MD5)
+        }
+
+    val parametersIndexedByName: Map<String, Parameter>
+        get() {
+            return parameters.associateBy { it.name }
+        }
 
     infix fun `has same definition`(other: Function): Boolean {
-        return other.getDefinition() == this.getDefinition()
+        return other.definition == this.definition
     }
 
     infix fun `is different from`(other: Function): Boolean {
diff --git a/src/main/kotlin/fr/postgresjson/migration/Function.kt b/src/main/kotlin/fr/postgresjson/migration/Function.kt
index 73f445a..a0a71aa 100644
--- a/src/main/kotlin/fr/postgresjson/migration/Function.kt
+++ b/src/main/kotlin/fr/postgresjson/migration/Function.kt
@@ -43,14 +43,14 @@ data class Function(
             } catch (e: CompletionException) {
                 val cause = e.cause
                 if (cause is GenericDatabaseException && cause.errorMessage.fields['C'] == "42P13") {
-                    connection.sendQuery("drop function ${down.getDefinition()}")
+                    connection.sendQuery("drop function ${down.definition}")
                     connection.sendQuery(up.script)
                 }
             }
 
             this::class.java.classLoader
                 .getResource("sql/migration/insertFunction.sql")!!.readText()
-                .let { connection.selectOne<MigrationEntity>(it, listOf(up.name, up.getDefinition(), up.script, down.script)) }
+                .let { connection.selectOne<MigrationEntity>(it, listOf(up.name, up.definition, up.script, down.script)) }
                 ?.let { function ->
                     executedAt = function.executedAt
                     doExecute = Action.OK
diff --git a/src/main/kotlin/fr/postgresjson/migration/Migrations.kt b/src/main/kotlin/fr/postgresjson/migration/Migrations.kt
index 4c7d2cb..e864862 100644
--- a/src/main/kotlin/fr/postgresjson/migration/Migrations.kt
+++ b/src/main/kotlin/fr/postgresjson/migration/Migrations.kt
@@ -133,17 +133,17 @@ class Migrations private constructor(
         Throwable("The file $path was not found", cause)
 
     fun addFunction(newDefinition: DefinitionFunction, callback: (Function) -> Unit = {}): Migrations {
-        val currentFunction = functions[newDefinition.name]
+        val currentFunction = functions[newDefinition.definitionHash]
         if (currentFunction === null || currentFunction `is different from` newDefinition) {
-            val oldDefinition = functions[newDefinition.name]?.up ?: newDefinition
-            functions[newDefinition.name] = Function(newDefinition, oldDefinition, connection).apply {
+            val oldDefinition = functions[newDefinition.definitionHash]?.up ?: newDefinition
+            functions[newDefinition.definitionHash] = Function(newDefinition, oldDefinition, connection).apply {
                 doExecute = Action.UP
             }
         } else {
-            functions[newDefinition.name]?.doExecute = Action.OK
+            functions[newDefinition.definitionHash]?.doExecute = Action.OK
         }
 
-        callback(functions[newDefinition.name]!!)
+        callback(functions[newDefinition.definitionHash]!!)
 
         return this
     }
@@ -215,7 +215,7 @@ class Migrations private constructor(
         return list.toMap()
     }
 
-    internal fun down(force: Boolean = false): Map<String, Status> {
+    fun down(force: Boolean = false): Map<String, Status> {
         val list: MutableMap<String, Status> = mutableMapOf()
         migrationsScripts.forEach {
             it.value.let { query ->
diff --git a/src/main/kotlin/fr/postgresjson/utils/md5.kt b/src/main/kotlin/fr/postgresjson/utils/md5.kt
new file mode 100644
index 0000000..d7bbba7
--- /dev/null
+++ b/src/main/kotlin/fr/postgresjson/utils/md5.kt
@@ -0,0 +1,12 @@
+package fr.postgresjson.utils
+
+import java.math.BigInteger
+import java.security.MessageDigest
+
+internal enum class Algorithm(name: String) {
+    MD5("MD5")
+}
+internal fun String.hash(algorithm: Algorithm): String {
+    val md = MessageDigest.getInstance(algorithm.name)
+    return BigInteger(1, md.digest(toByteArray())).toString(16).padStart(32, '0')
+}