Client constructor

content/03-reference/01-tools-and-interfaces/02-prisma-client/02-constructor.mdx

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+---
+title: 'Constructor'
+metaTitle: 'Prisma Client Constructor (Reference)'
+metaDescription: 'This page describes the Prisma Client constructor parameters.'
+---
+
+## Overview
+
+This page describes the Prisma Client constructor parameters.
+
+## `datasources`
+
+Use the `datasources` constructor parameter to programatically override the URL of a datasource - for example, as part of an integration test. To override a datasource:
+
+1. Define a datasources in the `prisma.schema` file. In the following example, there is a single datasource named `my_database`:
+
+   ```prisma
+   datasource my_database {
+    provider = "sqlite"
+    url      = env("DATABASE_URL")
+   }
+   ```
+
+   The `DATABASE_URL` environment variable defines the following value:
+
+   ```
+   DATABASE_URL="file:./dev.db"
+   ```
+
+   > **Note**: You must re-generate the Prisma Client each time you add or rename a datasource. Datasource names are included in the generated client.
+
+2. Instantiate a client and override the connection string of the `my_database` datasource:
+
+   ```ts
+   import { PrismaClient } from '@prisma/client'
+
+   const prisma = new PrismaClient({
+     datasources: {
+   |       my_database: 'file:./dev_qa.db',
+     },
+   })
+   ```
+
+> **Note**: If you define multiple datasources in `prisma.schema`, Prisma defaults to the first entry.
+
+See [Datasources](../prisma-schema/data-sources) for more information.
+
+## `log`
+
+Use the `log` constructor parameter to determine the type and level of logging. The following configuration raises an event each time the Prisma Client queries the database:
+
+```ts
+const prisma = new PrismaClient({
+  log: [{ emit: 'event', level: 'query' }],
+})
+```
+
+See [Logging](logging) for more information.
+
+## `errorFormat`
+
+Use the `errorFormat` constructor parameter to determine the level and formatting of errors returned by Prisma. The following configuration outputs raw error messages without formatting or extended information about the error:
+
+```ts
+const prisma = new PrismaClient({
+  errorFormat: 'minimal', // Defaults to 'pretty'
+})
+```
+
+See [Error formatting](error-formatting) for more information.