Create README.md

Author: SimpleProgramming

README.md

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+# Spring Boot AWS DynamoDB
+
+DynamoDB is a Document style database. In other words semi-structured database. It has the capability 
+to scale depending upon the size of data, And it supports 35 levels of nesting on data. Data is stored 
+in solid state drives, and is spread across 2 geographical datacenter so data can never be lost.
+
+DynamoDB supports two types of primary key attributes
+
+    single attribute - Hash Key/Partition Key
+    this hash key is used to calculate the hash value which is then used to determine the physical 
+    location where the data will be stored
+    no two keys can have same values in single attribute 
+    
+    composite attribute - Hash Key + Range Key/Sort Key
+    this is a combination of hash key and a range key.
+    two items can have same hash key but different range key
+
+You can use DynamoDB directly from the cloud environment or you can use the dynamodb local a downloadable version provided by amazon
+
+In this example, we are going to directly connect and work with the cloud version
+
+DynamoDBMapper is a Object mapper for domain-object interaction with DynamoDB.
+
+DynamoDBSaveExpression - you can use this to adding multiple expressions for your need. 
+For example, you may want to save only if an attribute has a particular value.
+
+ExpectedValue - it represent a condition to be compared with an attribute value